Introduction

Category I of the Praxis Special Education: Foundational Knowledge (5355) exam addresses human development and individual learning differences, accounting for 27% of the total score — 32 of the 120 questions. Competency 1A specifically focuses on human development and developmental milestones: the theories that explain how children grow, the predictable sequences of typical development across cognitive, language, social-emotional, and physical domains, the characteristics associated with each of the 13 IDEA disability categories, and the ways disability affects development across all domains. Mastery of this competency provides the conceptual foundation for everything else in special education practice — assessment, IEP goal-writing, instructional planning, and collaboration all depend on a deep understanding of how children develop and how disabilities alter that trajectory.

This lesson covers the major developmental theories tested on the Praxis 5355, detailed milestone sequences from birth through adolescence, the defining characteristics of each IDEA disability category, the critical principle of within-group variability, and how various disabilities affect each domain of development. The Praxis exam frequently presents scenario-based questions in which you must identify which theoretical framework best explains a teacher's decision, recognize whether a student's profile fits a particular disability category, or determine how a disability's impact on development should shape instructional choices. Understanding these concepts at a deep, applied level — not merely memorizing definitions — is the goal of this lesson.

Theories of Human Development

Developmental theory provides the conceptual lens through which special educators understand why children behave and learn as they do. The Praxis 5355 tests several foundational theories, and exam questions will often describe classroom scenarios and ask you to identify which theoretical perspective best applies. The five frameworks below are the most heavily tested.

Piaget's Cognitive Development Theory

Jean Piaget proposed that children actively construct knowledge through direct interaction with their environment. He described cognitive development as a series of qualitatively distinct stages, each characterized by a particular way of thinking that represents a fundamental reorganization of mental structure rather than simply the accumulation of more knowledge.

Sensorimotor Stage (birth–2 years): Infants and toddlers learn through sensory experience and motor action. The major achievement of this stage is object permanence — the understanding that objects continue to exist even when they are out of sight (typically achieved around 8–12 months). By the end of this stage, children begin to use mental representations.
Preoperational Stage (2–7 years): Children use symbols (language and pretend play) but cannot yet perform logical operations. Key features include egocentrism (difficulty taking another's perspective), centration (focusing on one dimension of a problem at a time), animism (attributing life to inanimate objects), and inability to conserve (understand that quantity remains constant despite changes in appearance). The classic conservation task — showing that pouring water into a differently shaped container doesn't change the amount — reveals the limits of preoperational thinking.
Concrete Operational Stage (7–11 years): Children can perform logical operations on concrete objects and events. They master conservation, can classify objects by multiple attributes simultaneously (classification), understand reversibility (the relationship between addition and subtraction), and can arrange objects in order (seriation). Thinking remains tied to physical reality; abstract reasoning is limited.
Formal Operational Stage (12+ years): Adolescents develop abstract reasoning, hypothetical-deductive thinking, and systematic problem-solving. They can reason about possibilities, not just realities, and engage in metacognition — thinking about their own thought processes.
Schemas, Assimilation, and Accommodation: Piaget described cognitive development as the ongoing refinement of schemas (mental frameworks). Children use assimilation to fit new information into existing schemas and accommodation to modify schemas when new information cannot be assimilated. The balance between these two processes — equilibration — drives cognitive growth.

Exam Connection: The Praxis 5355 may ask you to identify which Piagetian stage a student is functioning in based on a behavioral description, or to recognize why a student with an intellectual disability who is chronologically a teenager may be functioning at a preoperational level. Remember that Piaget viewed development as primarily driven by biological maturation and direct experience — the child is an active constructor of knowledge.

Vygotsky's Sociocultural Theory

Lev Vygotsky argued that cognitive development is fundamentally a social process — children learn by interacting with more knowledgeable others (parents, teachers, peers) and internalizing the tools and language of their culture. This perspective is especially influential in special education because it provides a framework for understanding how instruction, not just maturation, drives learning.

Zone of Proximal Development (ZPD): The ZPD is the range between what a child can accomplish independently (the lower boundary) and what the child can accomplish with support from a more knowledgeable other (the upper boundary). Effective instruction targets skills within the ZPD — too easy produces no growth, too difficult exceeds the learner's current capacity. For students with disabilities, accurately identifying the ZPD through dynamic assessment is essential for designing appropriate IEP goals.
Scaffolding: Scaffolding refers to the temporary, adjustable support a teacher or peer provides to help a learner accomplish a task within their ZPD. Effective scaffolding is calibrated to the learner's current level and gradually withdrawn (faded) as competence increases. Examples include graphic organizers, think-alouds, sentence starters, and physical prompts. Scaffolding is one of the most important concepts in special education instruction.
Private Speech: Young children often talk aloud to themselves while solving problems. Vygotsky viewed this "private speech" as an internalization of the social dialogue of instruction — children essentially direct themselves using language that originated in interactions with others. Private speech gradually becomes internalized as silent verbal thought by middle childhood. Children with language-based learning disabilities or ADHD may have difficulty with this internalization.
Language as a Tool: Vygotsky emphasized language as the primary cognitive tool through which humans think and regulate behavior. This has profound implications for students with speech/language impairments or autism spectrum disorder, whose language differences may affect not just communication but also self-regulation and thinking.
Mediated Learning: Humans do not interact with the world directly but through cultural tools and signs (language, number systems, writing). This is why literacy — a culturally constructed system — is so central to academic development and why students with reading disabilities face cascading challenges across all academic content areas.

Exam Connection: Vygotsky's framework is the theoretical basis for practices like peer-mediated learning, collaborative problem-solving, and instructional scaffolding — all of which appear on the Praxis 5355. Questions may ask you to identify the ZPD in a scenario or explain why a teacher gradually reduces prompting as a student masters a skill.

Erikson's Psychosocial Theory

Erik Erikson proposed that development unfolds across eight stages, each defined by a psychosocial crisis — a tension between two opposing outcomes. Successful navigation of each stage contributes to a healthy sense of identity and social-emotional competence; failure to resolve a stage leaves lasting psychological challenges. The first five stages are most relevant to school-age children and adolescents.

Trust vs. Mistrust (birth–18 months): Infants develop a basic sense of trust when caregivers are reliably responsive and nurturing. When caregiving is inconsistent or neglectful, mistrust develops. This foundational stage sets the stage for all subsequent attachment and relationship patterns — critical context for understanding children who have experienced early neglect or trauma.
Autonomy vs. Shame and Doubt (18 months–3 years): Toddlers develop a sense of independence and self-control through exploration. Overly restrictive or critical caregiving produces shame and self-doubt. Children with significant motor or cognitive disabilities may face particular challenges during this stage if their attempts at independence are frequently thwarted.
Initiative vs. Guilt (3–6 years): Preschoolers develop the capacity for purposeful activity and leadership. When initiative is consistently punished or criticized, children develop guilt about their desires and ambitions. For children who frequently fail at tasks due to learning difficulties, this stage can result in reduced initiative and learned helplessness.
Industry vs. Inferiority (6–12 years): School-age children focus on mastery of academic and social skills. Success builds a sense of competence (industry); repeated failure or comparison to peers produces feelings of inadequacy (inferiority). This is the most critical stage for children with learning disabilities, as ongoing academic struggle directly threatens their developing sense of industry. Special educators must build in multiple opportunities for success and emphasize growth over comparison.
Identity vs. Role Confusion (12–18 years): Adolescents explore who they are across multiple domains (academic, social, vocational). Students with disabilities may face particular identity challenges related to their disability label, social differences, and uncertainty about their adult roles. Transition planning during this stage is essential.

Exam Connection: The Praxis 5355 may present questions about why a student with a learning disability develops negative self-concept or avoids academic tasks. Erikson's Industry vs. Inferiority stage provides the theoretical explanation: chronic academic failure threatens the developing sense of competence. Questions may also address the role of emotional safety and relationship quality in supporting students through these developmental crises.

Bronfenbrenner's Ecological Systems Model

Urie Bronfenbrenner proposed that child development cannot be understood in isolation — it occurs within a nested system of environmental contexts that interact with and shape each other. This bioecological model is the theoretical foundation for family-centered practice, community-based supports, and the emphasis on collaboration in special education.

Microsystem: The immediate settings in which the child directly participates — family, classroom, peer group, neighborhood. The microsystem has the most direct influence on development. For students with disabilities, the quality of teacher-student relationships, family support, and peer acceptance within the microsystem are powerful determinants of outcomes.
Mesosystem: The relationships and interactions between different microsystems — such as the connection between home and school. When parents are actively involved in IEP meetings and communicate regularly with teachers, the mesosystem is strong. Breakdowns in home-school communication weaken the mesosystem and often undermine student progress.
Exosystem: Settings that affect the child indirectly — a parent's workplace, the school board's budget decisions, community service agencies. A parent who works two jobs may have less time for IEP involvement, and school district budget cuts may reduce available support services — both exosystem factors that affect a student's educational experience without the student being directly involved.
Macrosystem: Broader cultural values, laws, and social attitudes. IDEA, the ADA, and cultural beliefs about disability and education all operate at the macrosystem level. Cultural attitudes toward disability vary significantly across communities and affect how families respond to diagnosis, involvement in special education, and expectations for their children's futures.
Chronosystem: The dimension of time — how changes over time within systems affect development. A student who experiences a parent's divorce, a school change, or a new diagnosis at different points in development will experience different impacts depending on their developmental stage at the time.

Exam Connection: Bronfenbrenner's model explains why special education is not just about the student in isolation but requires family involvement, community partnerships, and awareness of cultural context. Praxis 5355 questions about collaboration with families, culturally responsive practice, and the impact of poverty or trauma on student development all reflect Bronfenbrenner's ecological framework.

Behavioral Theory (Behaviorism)

Behaviorism, developed by John Watson and extended by B.F. Skinner, focuses on observable behavior and the environmental events that control it. While cognitive and sociocultural theories have grown in prominence, behavioral principles remain foundational to special education practice, particularly for students with autism spectrum disorder, emotional and behavioral disorders, and intellectual disabilities.

Operant Conditioning: Skinner demonstrated that behavior is shaped by its consequences. Behaviors that are followed by positive consequences (reinforcement) increase in frequency; behaviors that are followed by negative consequences (punishment) decrease. This simple framework underlies Applied Behavior Analysis (ABA), token economies, behavioral contracts, and countless classroom management strategies used in special education.
Positive Reinforcement: Providing a desired consequence following a target behavior to increase its future probability. Effective reinforcers are individualized — what reinforces one student may be neutral or even aversive to another. Common reinforcers include verbal praise, preferred activities, tokens, and sensory input (for students with ASD).
Negative Reinforcement: Removing an aversive stimulus following a behavior to increase that behavior. A student who escapes a difficult writing task by engaging in disruptive behavior has been negatively reinforced — the disruption increased because it successfully removed the aversive demand. Understanding escape-maintained behavior is critical for designing effective behavior intervention plans (BIPs).
Punishment: Positive punishment adds an aversive stimulus following a behavior to reduce it (e.g., verbal reprimand); negative punishment removes a desired stimulus (e.g., loss of recess). IDEA emphasizes positive behavioral supports and discourages aversive interventions, particularly for students with disabilities.
Extinction: Withholding reinforcement for a previously reinforced behavior to reduce it. If a student's attention-seeking behavior has been maintained by teacher attention, systematically ignoring the behavior (while reinforcing appropriate alternatives) can extinguish it. Extinction often produces an initial "extinction burst" — a temporary increase in behavior before it decreases.
Antecedent-Behavior-Consequence (ABC) Analysis: The foundation of functional behavioral assessment (FBA). Identifying what happens before a behavior (antecedents) and after a behavior (consequences) reveals the function of the behavior — what it achieves for the student. Most behaviors serve one of four functions: access to tangibles, escape/avoidance, attention, or sensory stimulation.

Exam Connection: The Praxis 5355 frequently tests knowledge of reinforcement, the difference between positive and negative reinforcement (a commonly confused pair), and the application of behavioral principles in school settings. Remember: negative reinforcement is NOT punishment — it involves removing something unpleasant to increase a behavior.

Typical Developmental Milestones

Understanding typical developmental milestones is essential for identifying when development deviates from expected patterns — a core skill for special educators involved in child study teams, eligibility evaluations, and progress monitoring. The Praxis 5355 expects candidates to know milestone sequences across four domains: cognitive, language, social-emotional, and physical (motor), from infancy through adolescence.

Cognitive Development Milestones

Cognitive milestones reflect the development of thinking, memory, attention, problem-solving, and the ability to represent the world mentally. They follow the sequence described by Piaget but also include specific skill benchmarks assessed in educational and clinical settings.

Birth–12 months: Responds to familiar faces and voices; tracks moving objects; explores objects by mouthing and manipulating; demonstrates cause-and-effect understanding (shaking a rattle); develops object permanence (begins searching for hidden objects around 8–12 months); imitates simple gestures.
12–24 months: Uses trial-and-error problem-solving; engages in simple pretend play (feeding a doll); points to pictures in books when named; follows two-step directions with familiar routines; begins symbolic play; demonstrates basic sorting (puts like objects together).
2–3 years: Engages in elaborate pretend play with narrative sequences; matches shapes and colors; understands concepts of "more" and "less"; completes simple puzzles (3–4 pieces); sorts by one attribute (color or shape); begins to understand time concepts (today, tomorrow).
3–5 years: Counts 10 or more objects; understands quantity concepts (more, fewer, the same); identifies some letters; shows early phonological awareness (rhyming, syllable clapping); draws a person with at least 6 parts; understands time concepts (yesterday, today, tomorrow); asks "why" questions constantly (curiosity-driven inquiry).
5–7 years: Reads simple words; performs basic addition and subtraction with concrete objects; classifies objects by multiple attributes; demonstrates conservation of number (understands that 5 objects spread out is still 5); follows multi-step instructions; begins planning and self-monitoring during tasks.
7–12 years: Reads to learn across content areas; performs multi-step math operations; understands figurative language (idioms, metaphors); demonstrates logical reasoning with concrete problems; develops sustained attention for 20–30 minutes on structured tasks; engages in systematic study strategies.
12+ years: Abstract reasoning fully emerges; can consider hypothetical situations; engages in deductive reasoning; develops metacognitive strategies; plans and self-regulates multi-step academic projects; understands complex cause-and-effect relationships across social, historical, and scientific contexts.

Exam Connection: The Praxis 5355 may present a student profile and ask you to identify which cognitive milestones are delayed or absent. Remember that a student who has not achieved conservation by age 8 or who cannot engage in abstract reasoning by age 14 is demonstrating atypical cognitive development, which should prompt further evaluation.

Language and Communication Milestones

Language development spans receptive language (understanding what is heard) and expressive language (producing spoken, written, or signed communication). Receptive language consistently develops ahead of expressive language at every stage. Speech and language are distinct: speech refers to the physical production of sounds, while language refers to the rule-governed system of symbols and their meanings.

Birth–6 months: Responds to voice; startles to loud sounds; coos and makes vowel sounds; social smiling in response to familiar faces; begins turn-taking in vocal exchanges (protoconversation).
6–12 months: Babbles with consonant-vowel combinations (ma-ma, ba-ba); produces varied intonation patterns that mimic conversation; responds to own name; understands "no"; uses gestures (waving, pointing by 12 months); joint attention emerges (following caregiver's point or gaze).
12–18 months: First words appear (mama, dada, common objects); vocabulary of 5–15 words; understands simple instructions ("Come here," "Give me the ball"); uses gestures to augment communication; responds to simple questions.
18–24 months: Vocabulary grows rapidly (vocabulary explosion); uses 50+ words; begins combining two words ("more juice," "daddy go"); follows two-step commands; points to pictures when named; strangers can understand about 50% of speech.
2–3 years: Produces 3–4 word utterances; uses pronouns (I, you, me); asks simple questions; vocabulary of 200–1,000 words; strangers understand 75% of speech; uses plurals and past tense (with errors — "goed," "mouses").
3–5 years: Uses 4–6 word sentences; tells simple stories with beginning-middle-end; uses most phonemes correctly (some articulation errors persist until age 7–8); understands complex sentences; asks "why," "when," "how"; uses language for a variety of functions (requesting, commenting, questioning, narrating).
5–7 years: Speech is fully intelligible; produces complex sentences with conjunctions, relative clauses; understands figurative language beginning to emerge; phonological awareness is solid (can segment, blend, delete phonemes); reading acquisition underway.
7–12 years: Vocabulary expands dramatically through reading; understands and uses idioms, metaphors, sarcasm; produces extended discourse (multi-paragraph writing, multi-turn conversation); narrative structure becomes sophisticated.
12+ years: Metalinguistic awareness (can analyze language as an object); abstract language comprehension fully developed; argumentative and persuasive language emerges; registers shift appropriately across social contexts.

Exam Connection: Red flags the Praxis 5355 expects you to recognize: no babbling by 12 months, no single words by 16 months, no two-word phrases by 24 months, and any loss of previously acquired language skills at any age. These are automatic triggers for speech-language evaluation.

Social-Emotional Development Milestones

Social-emotional development encompasses the ability to form relationships, regulate emotions, understand others' perspectives, and navigate social interactions. This domain is foundational to all other learning — a child who cannot regulate emotions or form trusting relationships with teachers and peers cannot fully access academic instruction.

Birth–6 months: Social smiling (4–6 weeks); responds differentially to familiar vs. unfamiliar faces; beginning of attachment; expresses basic emotions (distress, interest, joy); participates in face-to-face social play.
6–12 months: Stranger anxiety emerges (6–9 months); separation anxiety increases; shows clear attachment preferences; social referencing (looks to caregiver to interpret ambiguous situations); joint attention established.
12–24 months: Plays alongside peers (parallel play) rather than with them; strong attachment to primary caregivers; imitates peer behavior; beginning of empathy (comforts others who appear distressed); self-recognition in mirror (18 months).
2–3 years: Begins cooperative play in brief episodes; asserting autonomy (strong-willed behavior); emotional outbursts common (tantrums) due to limited self-regulation and language; developing awareness of own gender identity; increasing interest in peer play.
3–5 years: Engages in cooperative play with role assignment; follows simple game rules; shows empathy; begins perspective-taking (though still limited); can identify basic emotions in others; self-regulation improving but easily overwhelmed; friendship formation begins.
5–7 years: Understands others' perspectives more accurately; navigates peer conflicts with words; group play with sustained rule-following; self-concept developing around academic and social competence; emotional regulation improves significantly.
7–12 years: Strong peer relationships with same-age companions; loyalty and fairness valued; self-esteem linked to perceived competence in school and social domains; social comparison becomes prominent; gender-segregated peer groups common.
12+ years: Identity development (Erikson's Identity vs. Role Confusion); peer group centrality; romantic relationships begin; emotional intensity increases with puberty; risk-taking behavior increases; development of moral reasoning and social justice awareness.

Exam Connection: The Praxis 5355 may ask about the relationship between attachment quality and later social-emotional development, or about why a student with an emotional behavioral disorder struggles with peer relationships. Understanding these developmental sequences helps you recognize when social-emotional development is significantly delayed or atypical.

Physical and Motor Development Milestones

Motor development follows two major principles: cephalocaudal development (control proceeds from head downward — head control precedes trunk control, which precedes leg control) and proximodistal development (control proceeds from the body's center outward — trunk control precedes shoulder, then elbow, then wrist, then finger control). These principles explain why children achieve gross motor milestones before fine motor milestones at every stage.

Birth–6 months: Lifts head in prone position (1–2 months); social smiling (4–6 weeks); rolls from stomach to back (4–5 months); reaches and grasps objects; sits with support; palmar grasp (4–5 months).
6–12 months: Sits independently (6–8 months); crawls (8–10 months); pulls to standing; cruises along furniture; pincer grasp emerges (9–12 months); transfers objects hand-to-hand; first steps (9–15 months range).
12–24 months: Walking independently; climbing stairs with support (2 feet per step); runs (though unsteadily); throws a ball; scribbles with crayon; stacks 2–4 blocks; turns pages (sometimes several at once).
2–3 years: Runs smoothly; jumps with both feet; kicks a ball; rides a tricycle; walks up and down stairs alternating feet; draws circles and crosses; strings large beads; uses spoon and fork.
3–5 years: Hops on one foot; skips; catches a bounced ball; draws a recognizable person; cuts with scissors; begins writing letters (though often reversed and inconsistently sized); dresses and undresses independently.
5–7 years: Refined running, jumping, hopping, and skipping; rides bicycle; ties shoes; forms letters and numbers consistently; handwriting becomes legible; manipulates small objects with precision.
7–12 years: Athletic skill refinement; team sports participation; fine motor precision for cursive writing and detailed artwork; developing strength and endurance; puberty onset at the end of this range for many students.
12+ years: Puberty-related physical changes (may temporarily affect coordination); adult-level motor capacity developing; fine motor skills fully refined.

Exam Connection: The Praxis 5355 may present a student who cannot perform motor tasks expected at their age — for instance, a 7-year-old who cannot cut with scissors or a 10-year-old whose handwriting remains illegible. These motor differences are relevant to determining whether a student needs occupational therapy, whether accommodations like keyboard access are appropriate, or whether motor delays are a characteristic of their primary disability category.

The 13 IDEA Disability Categories

The Individuals with Disabilities Education Act (IDEA) establishes 13 disability categories through which students ages 3–21 may qualify for special education services. The Praxis 5355 expects candidates to know the defining characteristics, eligibility criteria, and educational implications of each category. Students must not only have a disability that fits one of these categories but must also demonstrate that the disability adversely affects their educational performance and that they require specially designed instruction.

Intellectual Disability (ID)

Characterized by significant limitations in both intellectual functioning (typically IQ below 70–75) and adaptive behavior, manifesting before age 18. Adaptive behavior encompasses conceptual skills (reading, money management, time concepts), social skills (interpersonal skills, responsibility, self-esteem), and practical skills (activities of daily living, occupational skills).

Mild ID (IQ 55–70): Most students with mild ID learn academic skills up to approximately the 6th grade level with appropriate support. They typically require support with complex social and financial decisions in adulthood but can live semi-independently.
Moderate ID (IQ 40–55): Functional academic skills (reading survival words, functional math) are achievable. Adults typically require supported employment and supervised living arrangements.
Severe ID (IQ 25–40): Communication, self-care, and safety skills are primary instructional targets. Extensive support is required across settings.
Profound ID (IQ below 25): Intensive, lifelong support is required for all basic life functions. Instruction focuses on basic communication, sensory responses, and comfort.
Educational implications: Differentiated curriculum, task analysis, systematic instruction, community-based instruction, functional curriculum, supported employment transition planning.

Specific Learning Disability (SLD)

A disorder in one or more of the basic psychological processes involved in understanding or using language (spoken or written), which manifests as significant difficulty in listening, thinking, speaking, reading, writing, spelling, or doing mathematical calculations. SLD is NOT due to intellectual disability, sensory impairment, emotional disturbance, cultural factors, environmental disadvantage, or limited English proficiency.

Types: Dyslexia (reading), dysgraphia (written expression), dyscalculia (mathematics), plus SLDs affecting listening comprehension, oral expression, and basic reading skills.
Identification approaches: Discrepancy model (significant gap between IQ and achievement) and Response to Intervention/Multi-Tiered Support Systems (RTI/MTSS), which identifies students who fail to respond adequately to evidence-based general education interventions.
Educational implications: Explicit, systematic instruction in the deficit area; assistive technology; extended time; reduced-distraction environment; multisensory instructional methods.
SLD is the largest IDEA category, representing approximately 33–35% of students receiving special education services.

Speech or Language Impairment (SLI)

A communication disorder — including stuttering, impaired articulation, language impairment, or voice impairment — that adversely affects educational performance. This category is distinct from autism spectrum disorder (which may include communication differences) and is the second most common IDEA category.

Articulation disorders: Difficulty producing specific speech sounds correctly (substitutions, omissions, distortions). Common errors include /r/ and /l/ persisting beyond the typical developmental window.
Fluency disorders: Disruptions in the flow of speech, including stuttering (repetitions, prolongations, blocks) and cluttering (rapid, irregular speech rate).
Language disorders: Difficulties with the form of language (phonology, morphology, syntax), content (semantics/vocabulary), or use (pragmatics/social language). Language disorders may affect both receptive and expressive language.
Voice disorders: Abnormal pitch, quality, or loudness affecting social communication.
Educational implications: Services provided by a speech-language pathologist (SLP); classroom accommodations for oral expression and listening comprehension; assistive/augmentative communication (AAC) for students with severe language impairments.

Emotional Disturbance (ED)

Characterized by one or more of the following conditions over a long period of time and to a marked degree that adversely affects educational performance: inability to learn not explained by other factors; inability to build or maintain satisfactory interpersonal relationships; inappropriate types of behavior or feelings; pervasive mood of unhappiness or depression; tendency to develop physical symptoms or fears associated with school or personal problems. Includes schizophrenia.

Does NOT include: Social maladjustment (conduct disorder without emotional disturbance, per IDEA's controversial exclusion clause — though this remains debated in the field).
Common conditions within ED: Anxiety disorders, depression, bipolar disorder, oppositional defiant disorder, conduct disorder, and schizophrenia.
Educational implications: Positive behavioral supports and interventions (PBIS); therapeutic supports; social-emotional learning curricula; structured, predictable environments; crisis intervention plans; collaboration with mental health professionals.
Important distinction: Behavior must be chronic, severe, and pervasive (not just a response to temporary circumstances) and must adversely affect educational performance to qualify under ED.

Autism Spectrum Disorder (ASD)

A developmental disability characterized by persistent deficits in social communication and social interaction across multiple contexts, combined with restricted, repetitive patterns of behavior, interests, or activities. Symptoms must be present in the early developmental period (though they may not fully manifest until social demands exceed capacity) and cause clinically significant impairment in social, occupational, or other important areas of functioning.

Social communication deficits: Difficulties with social-emotional reciprocity (back-and-forth conversation, sharing interests), nonverbal communicative behaviors (eye contact, facial expressions, gestures), and developing/maintaining relationships.
Restricted/repetitive behaviors (RRBs): Stereotyped or repetitive motor movements/speech; insistence on sameness; highly restricted/fixated interests; hyper- or hyporeactivity to sensory input.
Wide spectrum: ASD ranges from individuals who are nonspeaking with significant intellectual disability to highly verbal individuals with average or above-average IQ. All presentations share the core features of social communication differences and RRBs, but severity and manifestation vary enormously.
Educational implications: Visual supports; structured environments; explicit social skills instruction; ABA-based interventions; sensory accommodations; AAC for nonspeaking students; transition planning; strength-based approaches capitalizing on intense interests.

Orthopedic Impairment (OI)

A severe orthopedic impairment that adversely affects educational performance. Includes impairments caused by congenital anomalies (clubfoot, absence of a limb), impairments caused by disease (poliomyelitis, bone tuberculosis), and impairments from other causes (cerebral palsy, amputations, fractures or burns causing contractures).

Cerebral palsy (CP) is the most common cause of OI in school-aged students — a group of permanent movement disorders appearing in early childhood due to brain damage before, during, or shortly after birth.
Educational implications: Physical accessibility; assistive technology (switches, eye-gaze devices, power wheelchairs); adapted physical education; occupational therapy for fine motor and daily living skills; physical therapy for mobility; alternative assessment methods.

Traumatic Brain Injury (TBI)

An acquired injury to the brain caused by an external physical force, resulting in total or partial functional disability or psychosocial impairment that adversely affects educational performance. TBI applies to open or closed head injuries resulting in impairments in cognition, language, memory, attention, reasoning, abstract thinking, judgment, problem-solving, sensory/perceptual/motor abilities, psychosocial behavior, physical functions, information processing, or speech.

Does NOT include: Brain injuries that are congenital or degenerative, or brain injuries induced by birth trauma.
Educational implications: TBI recovery is often nonlinear — students may show improvement over time. Instruction must be flexible and re-evaluated frequently. Cognitive fatigue, memory difficulties, and behavior changes are common challenges. Extended time, reduced workload, frequent breaks, and explicit memory strategies are key supports.

Other Health Impairment (OHI)

Having limited strength, vitality, or alertness (including heightened alertness to environmental stimuli) that results in limited alertness with respect to the educational environment, due to chronic or acute health problems such as asthma, attention deficit hyperactivity disorder (ADHD), diabetes, epilepsy, heart conditions, hemophilia, lead poisoning, leukemia, nephritis, rheumatic fever, sickle cell anemia, and Tourette syndrome.

ADHD is the most common condition served under OHI, though students with ADHD may also qualify under other categories (SLD, ED) if those conditions also apply.
Educational implications: Vary by the specific health condition. For ADHD: preferential seating, reduced-distraction environment, chunked assignments, movement breaks, behavioral supports. For epilepsy: seizure response plans, seizure diary, medication administration. For diabetes: blood glucose monitoring, snack access, flexibility for health management.

Visual Impairment Including Blindness (VI)

An impairment in vision that, even with correction, adversely affects educational performance. Includes both partial sight and blindness.

Educational implications: Braille instruction (for students with insufficient functional vision for print); large print materials; magnification devices; orientation and mobility instruction; screen reader technology; expanded core curriculum (ECC) addressing disability-specific skills such as social interaction, recreation/leisure, and use of assistive technology.
Orientation and mobility (O&M) specialists provide instruction in safe, independent travel — a related service unique to students with visual impairments.

Hearing Impairment (HI) and Deafness

Deafness means a hearing impairment so severe that the student is impaired in processing linguistic information through hearing, with or without amplification, that adversely affects educational performance. Hearing impairment refers to impairment in hearing (whether permanent or fluctuating) that adversely affects educational performance but is not included under the definition of deafness.

Educational implications: Sign language interpreter services; FM systems; captioning; audiological services; speech-language therapy; social-emotional support (communication access in peer interactions); Deaf culture and identity considerations; ASL instruction when appropriate.
Communication approaches: The field involves significant ongoing debate about oral/spoken language approaches, sign-supported speech, and bilingual-bicultural (ASL/English) approaches. Special educators must be culturally responsive and involve families in communication decisions.

Deaf-Blindness (DB)

A combination of hearing and visual impairments causing such severe communication and other developmental and educational needs that they cannot be accommodated in programs solely for children with deafness or children with blindness.

Educational implications: Interveners (one-on-one support persons trained in deaf-blind communication); tactile communication systems (tactile sign language, objects of reference, braille); highly specialized, intensive supports; state deaf-blind technical assistance projects provide consultation.
Note: Students with deaf-blindness do not need to be completely deaf and completely blind — the combination of vision and hearing losses must together create the severe educational impact described in the definition.

Multiple Disabilities (MD)

Concomitant impairments (such as intellectual disability combined with orthopedic impairment) the combination of which causes such severe educational needs that they cannot be accommodated in programs designed solely for one of the impairments. Does not include deaf-blindness (which has its own category).

Educational implications: Highly individualized, team-based instruction; integrated therapy services; functional curriculum; augmentative and alternative communication (AAC); intensive support across all settings; person-centered planning for transition.

Developmental Delay (DD)

A category available for children ages 3–9 (and at states' discretion, up to age 10) who are experiencing significant developmental delays in one or more areas: physical development, cognitive development, communication development, social or emotional development, or adaptive development.

Purpose: Allows young children to receive early childhood special education services while evaluation continues to determine whether a more specific categorical label applies. This avoids premature labeling and allows time for intervention to demonstrate its effectiveness.
Important: States set their own definitions for what constitutes a "significant developmental delay" — criteria vary by state. Once a student reaches the maximum age for DD eligibility in their state, they must qualify under a specific IDEA category to continue receiving services.

Similarities and Differences Among Students with Disabilities

One of the most important principles in special education — and one directly tested on the Praxis 5355 — is that disability categories describe groups of students who share certain characteristics, but there is enormous variability within every group. No two students with the same disability category are identical in their strengths, challenges, or support needs.

Within-Group Variability and Heterogeneity

Within-group variability refers to the range of performance, characteristics, and needs among students who share a disability label. This variability is a defining feature of every IDEA category, not an exception.

ASD example: The autism spectrum includes a student who is nonspeaking, requires total assistance for daily living, and engages in intense self-stimulatory behavior alongside a student who is highly verbal, attends general education classes with minimal support, and has an advanced technical interest. Both students have ASD, but their educational needs are almost entirely different.
SLD example: Students with specific learning disability may have average or above-average cognitive ability alongside a severe deficit in one academic area (reading decoding), or they may have a profile of multiple academic weaknesses. The term "learning disabled" does not describe a uniform population.
ID example: Even within the "mild intellectual disability" range, students vary enormously in their adaptive behavior strengths, communication profiles, behavioral patterns, and academic potential. Curriculum decisions must be driven by individual assessment, not categorical assumptions.
Practical implication: The IEP is individualized precisely because the disability label alone does not prescribe instruction. Effective special educators use assessment data to understand each student's unique profile of strengths and needs.

Exam Connection: The Praxis 5355 tests whether candidates understand that disability categories are not homogeneous groups. Questions may present a scenario in which an educator makes a decision based on a student's label alone (without considering the individual's actual profile) and ask you to identify the problem with that approach.

Person-First Language and Identity-First Language

Person-first language places the person before the disability — "student with autism" rather than "autistic student" or "autistic child." The intent is to emphasize the person's humanity and individuality before their disability status. Person-first language has been the standard in special education professional practice and in IDEA itself for decades.

Examples of person-first language: "student with intellectual disability" (NOT "intellectually disabled student"), "child who is blind" (NOT "blind child"), "individual with autism spectrum disorder" (NOT "autistic individual").
Identity-first language: Many members of the Deaf community and many autistic self-advocates strongly prefer identity-first language ("autistic person," "Deaf person"), arguing that disability is an integral part of their identity, not something separate from them. The Praxis 5355 primarily reflects person-first language conventions, but candidates should be aware that identity-first language preferences exist and are respected within communities.
On the Praxis exam: Use person-first language unless the question specifically involves Deaf culture or a community that has expressed a preference for identity-first language. In professional documentation (IEPs, evaluation reports), person-first language is the standard.

Avoiding Stereotyping and Strength-Based Perspectives

Effective special educators resist applying categorical stereotypes and instead approach each student from a strength-based perspective — identifying what the student can do and building from that foundation rather than focusing exclusively on deficits.

Avoiding stereotyping: Not all students with ASD have savant skills, not all students with Down syndrome are affectionate and social, and not all students with learning disabilities have low self-esteem. Category characteristics describe group-level tendencies, not individual certainties.
Strength-based assessment: Uses ecological inventories, portfolio assessment, and student interviews to identify genuine strengths across academic, social, communicative, and functional domains. Strengths become the foundation for instructional planning and serve as motivational levers.
Universal Design for Learning (UDL): A strength-based, proactive approach to curriculum design that anticipates learner variability and provides multiple means of engagement, representation, and action/expression from the outset, rather than retrofitting accommodations after instruction fails.
Cultural responsiveness: Student strengths, communication styles, and learning preferences are shaped by cultural background. Effective special educators recognize cultural assets (bilingualism, collectivist values, oral tradition) as strengths rather than deficits.

Impact of Disability on Overall Development

Disabilities rarely affect a single developmental domain in isolation. Understanding how different disability categories affect cognitive, language, social-emotional, and physical development — including secondary characteristics and co-occurring conditions — is essential for comprehensive IEP planning and the content of the Praxis 5355.

How Intellectual Disability Affects Development Across Domains

Cognitive: Reduced capacity for abstract reasoning, working memory limitations, slower rate of skill acquisition, difficulty generalizing learned skills to new settings or contexts. Information processing is slower — students may require more repetition and distributed practice than peers.
Language: Delayed language acquisition; receptive language typically stronger than expressive language; limited syntactic complexity; vocabulary limited relative to age peers; pragmatic language (social use of language) may be relatively stronger in mild ID.
Social-emotional: May have age-appropriate social desires (wanting friendships, romantic relationships) but limited social skills to achieve them; susceptibility to peer victimization and social exploitation; emotional regulation typically developing on a slower timeline; risk of co-occurring depression and anxiety due to awareness of difference.
Physical/motor: Many students with mild-moderate ID have typical motor development; some syndromic causes (Down syndrome, Angelman syndrome) are associated with hypotonia (low muscle tone), gross motor delays, and fine motor challenges.
Secondary characteristics: Heightened risk of bullying; susceptibility to false confessions and social manipulation; disproportionate rates of co-occurring ADHD, anxiety disorders, and behavioral challenges.

How Autism Spectrum Disorder Affects Development Across Domains

Cognitive: Cognitive profiles are highly variable — some students have intellectual disability, some have average IQ, some have above-average IQ. Many students with ASD have an uneven cognitive profile (islets of exceptional ability alongside significant deficits). Executive function difficulties (planning, flexibility, working memory) are very common regardless of IQ level.
Language: Range from completely nonspeaking to highly verbal. Even verbal students may have significant pragmatic language difficulties (difficulty with conversation turn-taking, understanding nonliteral language, adjusting register). Echolalia (immediate or delayed repetition of heard speech) is common in developing communicators with ASD.
Social-emotional: Core deficits in social communication and reciprocity; difficulty reading nonverbal social cues; theory of mind differences (difficulty understanding others' mental states, perspectives, and intentions); may have intense desire for social connection despite social skill challenges; co-occurring anxiety disorders are extremely common (estimated 40–50% of individuals with ASD).
Physical/motor: Sensory processing differences affect responses to sensory input (hyper- or hyposensitivity to sound, touch, taste, vestibular input, proprioception); fine and gross motor differences common; gastrointestinal issues have a high prevalence in ASD; seizure disorders co-occur in approximately 30% of individuals with ASD.

How Specific Learning Disability Affects Development Across Domains

Cognitive: Average to above-average overall cognitive ability, but significant weaknesses in one or more specific cognitive processes (phonological processing, processing speed, working memory, rapid automatic naming). The discrepancy between potential and achievement is characteristic of SLD.
Language: Reading-based SLDs (dyslexia) involve deficits in phonological awareness, phonological memory, and/or rapid naming that impair the reading decoding process. Language-based SLD affects listening comprehension and expressive language as well as literacy.
Social-emotional: Chronic academic failure significantly impacts self-esteem and self-efficacy. Rates of anxiety and depression are elevated. Learned helplessness — the belief that effort will not produce success — is a risk when students repeatedly fail despite effort. Teacher-student relationship quality is a powerful protective factor.
Physical/motor: Dysgraphia (written expression SLD) frequently co-occurs with fine motor difficulties. Sensory processing differences may co-occur. Overall physical development is typically not directly affected by SLD.

How Emotional and Behavioral Disabilities Affect Development Across Domains

Cognitive: Direct effects on learning are mediated through attention, working memory, and executive function. Anxiety consumes cognitive resources (worry thoughts intrude on task engagement). Depression reduces motivation, energy, and information processing speed. ADHD directly impairs sustained attention, impulse control, and working memory.
Language: Social communication is often affected — students with ED may misinterpret social situations (hostile attribution bias: interpreting neutral peer behavior as threatening), have difficulty with pragmatic language, or use language that escalates rather than de-escalates conflict.
Social-emotional: The primary domain affected. Difficulty forming and maintaining relationships; poor emotional regulation; low frustration tolerance; co-occurring substance use (adolescence); trauma histories are prevalent (adverse childhood experiences are common among students with ED).
Physical/motor: Somatic complaints (headaches, stomachaches) are common. Physical manifestations of anxiety include rapid heartbeat, shortness of breath, and nausea. Depression may manifest as fatigue, changes in appetite, and psychomotor slowing.

Co-Occurring Conditions and Secondary Characteristics

Many students with disabilities have co-occurring conditions — two or more qualifying conditions that affect development simultaneously. Understanding co-occurrence is important for designing comprehensive, individualized supports.

ASD + ID: Approximately 31–37% of individuals with ASD also have intellectual disability. This combination requires particularly comprehensive planning, including AAC, structured environments, and intensive behavioral supports.
SLD + ADHD: Up to 30–50% of students with ADHD also have co-occurring SLD. Both conditions affect academic performance but require different intervention approaches (behavioral supports for ADHD, evidence-based reading instruction for dyslexia).
ID + psychiatric disorders: Rates of co-occurring psychiatric disorders in individuals with ID are 3–4 times higher than in the general population (a phenomenon called "dual diagnosis" in this context). Diagnosis can be challenging because students may have limited ability to describe internal experiences.
TBI + ED: Traumatic brain injury frequently results in emotional and behavioral changes, including irritability, impulsivity, depression, and anxiety. These behavioral effects may be misinterpreted as willful misbehavior without understanding the neurological basis.
Physical disabilities + secondary psychological effects: Students with orthopedic impairments, chronic illness (OHI), or sensory disabilities face a higher risk of depression, anxiety, and social isolation due to physical limitations, medical procedures, and social exclusion.

Exam Connection: The Praxis 5355 may ask you to recognize secondary characteristics or co-occurring conditions in a student scenario. Remember that disability impacts ripple across domains — a student with a physical disability may also need social-emotional support, and a student with an emotional disability may also need cognitive supports.

Key Takeaways

Piaget's stages are sequential and qualitative: Children progress through sensorimotor, preoperational, concrete operational, and formal operational stages — each representing a fundamentally different way of thinking, not just more information.
Vygotsky's ZPD drives effective instruction: Instruction should target the zone between independent and assisted performance; scaffolding provides temporary support within the ZPD and is gradually faded as competence grows.
Erikson's Industry vs. Inferiority is critical for school-age students: Chronic academic failure threatens the development of industry (competence) and may produce lasting inferiority; special educators must engineer success and build self-efficacy.
Bronfenbrenner's ecology explains why context matters: Family, school, community, culture, and time all shape development; effective special education addresses multiple ecological levels, not just the student in isolation.
Behavioral principles underlie many special education practices: Reinforcement (positive and negative), extinction, and functional behavioral assessment are foundational tools; negative reinforcement removes something unpleasant to increase behavior — it is NOT punishment.
Language milestones provide critical red flags: No babbling by 12 months, no words by 16 months, no two-word phrases by 24 months, and any loss of language are automatic referral triggers.
The 13 IDEA categories each have distinct definitional criteria: SLD is the largest category; Developmental Delay is time-limited (ages 3–9 or 10); Emotional Disturbance requires chronic, pervasive impact on educational performance; TBI requires an external physical cause.
Within-group variability is enormous: Disability labels describe group tendencies, not individual certainties; the IEP must be built from individual assessment data, not categorical assumptions.
Person-first language is the professional standard: Place the person before the disability in professional contexts; be aware that some disability communities (Deaf community, many autistic self-advocates) prefer identity-first language.
Disability impacts ripple across all developmental domains: No disability affects only one domain — special educators must assess and support the whole student, including cognitive, language, social-emotional, physical, and adaptive development.
Co-occurring conditions are common: ASD + ID, SLD + ADHD, TBI + ED, and many other combinations require educators to plan for multiple, overlapping sets of needs simultaneously.
Secondary characteristics are predictable: Understand that social isolation, depression, anxiety, and reduced self-esteem are common secondary characteristics for students across disability categories — these require proactive support, not just academic intervention.

What You'll Learn

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