11.1 High-Incidence Disabilities: SLD, ADHD/OHI, and Speech/Language Impairments

11.1 High-Incidence Disabilities: SLD, ADHD/OHI, and Speech/Language Impairments

Quick Summary: High-incidence disabilities represent approximately 70% to 80% of all students served under the Individuals with Disabilities Education Act (IDEA). This population encompasses three primary categories: Specific Learning Disabilities (SLD), Other Health Impairments (OHI, predominantly Attention-Deficit/Hyperactivity Disorder), and Speech or Language Impairments (SLI). While students with high-incidence disabilities spend the majority of their school day in general education classrooms alongside neurotypical peers, they require specialized academic instruction, targeted cognitive scaffolds, executive functioning supports, and explicit skill remediation. This section explores statutory definitions under 34 CFR § 300.8, cognitive profiles, clinical subtypes (dyslexia, dyscalculia, dysgraphia), the critical boundary between medical and educational diagnoses, motor versus linguistic communication disorders, and evidence-based instructional accommodations.

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Specific Learning Disabilities (SLD): Prevalence and Federal Definition

Specific Learning Disabilities (SLD) constitute the largest single disability category under IDEA, representing approximately 35% to 40% of all students receiving special education services nationwide and in Georgia public schools. Under federal regulations (34 CFR § 300.8(c)(10)), a specific learning disability is defined as:

"A disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, that may manifest itself in the imperfect ability to listen, think, speak, read, write, spell, or to do mathematical calculations, including conditions such as perceptual disabilities, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia."

The Core Cognitive Profile of SLD

A defining characteristic of SLD is that the student possesses average to above-average general intellectual ability (typically a Full-Scale IQ of 85 or higher, falling within or above the standard normal range) alongside a severe, unexpected deficit in one or more specific academic achievement areas. The learning difficulty is not attributable to generalized cognitive impairment, but rather stems from an underlying deficit in basic psychological processes, such as:

• Phonological Processing: Difficulty perceiving, isolating, blending, and manipulating the discrete sound structures (phonemes) of language.
• Working Memory: Limited capacity to temporarily hold and manipulate verbal or visual information during complex cognitive tasks.
• Processing Speed: Slower cognitive throughput when performing automatic, routine visual or symbolic tasks.
• Visual-Spatial Processing: Challenges analyzing, interpreting, and mentally manipulating spatial arrays, geometric figures, and mathematical notations.
• Executive Functioning: Deficits in working memory, cognitive flexibility, self-monitoring, and cognitive organization.

Mandatory Exclusionary Criteria

Under IDEA (34 CFR § 300.8(c)(10)(ii)), an eligibility committee cannot classify a student under SLD if the severe academic deficit is primarily the result of:

1. A visual, hearing, or motor disability;
2. Intellectual disability;
3. Emotional disturbance;
4. Cultural factors;
5. Environmental or economic disadvantage; or
6. Limited English proficiency (LEP / English Learner status).

Furthermore, federal and Georgia rules mandate explicit documentation that the student's underachievement is not due to a lack of appropriate instruction in essential reading components (phonemic awareness, phonics, vocabulary, fluency, and comprehension) or mathematics.

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Subtypes of Specific Learning Disabilities: Dyslexia, Dyscalculia, and Dysgraphia

While IDEA encompasses eight statutory academic deficit areas (oral expression, listening comprehension, written expression, basic reading skills, reading fluency skills, reading comprehension, mathematical calculation, and mathematical problem-solving), clinical and educational practice categorizes SLD into three prominent neurobiological subtypes:

1. Dyslexia (Reading-Based SLD)

Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction.

• Primary Manifestations: Weak phonemic awareness (e.g., segmenting, blending, deleting phonemes), slow and inaccurate pseudoword/nonsense word decoding, impaired rapid automatized naming (RAN), labor-intensive reading rate, and orthographic mapping deficits that prevent automatic sight-word recognition.
• Secondary Consequences: Reduced reading comprehension, limited vocabulary growth, reduced reading stamina, and spelling difficulties that persist into adulthood.
• Evidence-Based Pedagogical Interventions: Structured Literacy grounded in the Science of Reading; explicit, systematic, sequential, and cumulative instruction in phonological awareness and synthetic phonics (e.g., Orton-Gillingham-based methodologies, Wilson Reading System); multisensory tracing routines; syllable division rules; and morphology instruction.

2. Dyscalculia (Mathematics-Based SLD)

Dyscalculia is a neurodevelopmental learning disability affecting the acquisition of arithmetic skills and mathematical reasoning. It involves a fundamental disruption in the brain's intuitive "number sense."

• Primary Manifestations: Inability to subitize (instantly perceive the quantity of a small group of items without counting), persistent reliance on finger counting well past developmental milestones, difficulty understanding the mental number line, confusion regarding arithmetic symbols ($+$, $-$, $\times$, $\div$), severe deficits in automatic retrieval of basic math facts, spatial disorientation when aligning multi-digit calculation columns, and difficulty grasping mathematical word problems.
• Evidence-Based Pedagogical Interventions: The Concrete-Representational-Abstract (CRA) instructional continuum (using hands-on manipulatives like base-ten blocks, transitioning to pictorial representations, before introducing abstract numerical algorithms); Schema-Based Instruction (SBI) for word problems; explicit visual number lines; graph paper to maintain column alignment; and visual reference charts for math facts.

3. Dysgraphia (Writing-Based SLD)

Dysgraphia is an impairment in written expression characterized by neurodevelopmental deficits in the fine-motor transcription and orthographic coding necessary to produce legible, automatic written text.

• Primary Manifestations: Highly irregular letter sizing, inconsistent spacing between words and letters, labored and painfully slow handwriting speed, awkward pencil grip and hand cramping (graphomotor fatigue), inability to store and retrieve the visual forms of letters (orthographic memory), severe spelling phonetic errors, and a vast discrepancy between rich oral expression and sparse, disorganized written output.
• Evidence-Based Pedagogical Interventions: Explicit instruction in letter formation using tactile mediums; ergonomic pencil grips and slant boards; graphic organizers for pre-writing; assistive technology including speech-to-text (dictation) software, word prediction, and touch-typing instruction; and testing accommodations permitting oral responses or scribe support.

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Psychoeducational Identification: Severe Discrepancy vs. RTI/MTSS and PSW Models

Historically, school psychologists identified SLD using the Severe Discrepancy Model. This method required documenting a statistically significant mathematical discrepancy (typically 1.5 to 2.0 standard deviations, equivalent to 15 to 30 standard score points) between a student's Full-Scale IQ (measured by an intelligence battery like the WISC-V) and their standardized academic achievement score (measured by the WIAT-4 or Woodcock-Johnson IV).

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|                    CRITIQUE OF THE HISTORICAL SEVERE DISCREPANCY MODEL                  |
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|  - Widely criticized as a "WAIT-TO-FAIL" approach: Young students in grades K-2 rarely |
|    exhibit a large enough statistical gap between IQ and reading scores to qualify.     |
|  - Did not inform targeted instruction: Documenting a point gap provided zero diagnostic|
|    guidance on which specific phonological or cognitive sub-skills required remediation.|
|  - Disproportionate representation: Over-identified culturally and linguistically      |
|    diverse learners due to inherent cultural and language biases in IQ testing.        |
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The Response to Intervention (RTI) / MTSS Framework

IDEA 2004 reformed this system by establishing that states cannot require the use of a severe discrepancy and must permit the use of a process based on the child's response to scientific, research-based intervention (34 CFR § 300.307). Under the RTI / Multi-Tiered System of Supports (MTSS) identification model, SLD is determined through a dual-discrepancy framework:

1. Discrepancy in Level: The student's academic performance level is significantly below that of age- or grade-level peers on Curriculum-Based Measurement (CBM) probes.
2. Discrepancy in Slope (Rate of Growth): Despite receiving high-intensity, research-based Tier 2 and Tier 3 interventions delivered with verified fidelity, the student's rate of progress over time (slope on an aim line) is insufficient to close the academic gap.

Patterns of Strengths and Weaknesses (PSW)

Many Georgia school districts utilize the Patterns of Strengths and Weaknesses (PSW) model (such as the Concordance-Discordance Model). PSW evaluates cognitive processing batteries to confirm that the student exhibits:

• An area of cognitive strength (intact general intelligence and processing abilities falling within the average range);
• An area of academic weakness (normative academic failure in reading, math, or writing); and
• An area of specific psychological processing weakness that is theoretically and empirically linked to the academic failure (e.g., phonological processing weakness directly causing basic reading failure).

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Other Health Impairment (OHI) and Attention-Deficit/Hyperactivity Disorder (ADHD)

Under federal regulations (34 CFR § 300.8(c)(9)), Other Health Impairment (OHI) is defined as:

"Having limited strength, vitality, or alertness, including a heightened alertness to environmental stimuli, that results in limited alertness with respect to the educational environment, that is due to chronic or acute health problems such as asthma, attention deficit disorder or attention deficit hyperactivity disorder, diabetes, epilepsy, a heart condition, hemophilia, lead poisoning, leukemia, nephritis, rheumatic fever, sickle cell anemia, and Tourette syndrome; and adversely affects a child's educational performance."

ADHD as the Primary Driver of OHI

Although the federal category lists numerous medical conditions, the overwhelming majority of students served under OHI qualify due to Attention-Deficit/Hyperactivity Disorder (ADHD). Under the DSM-5, ADHD is a neurodevelopmental disorder defined by persistent patterns of inattention and/or hyperactivity-impulsivity that interfere with functioning or development across multiple settings (home, school, social). It encompasses three clinical presentations:

1. Predominantly Inattentive Presentation: Characterized by difficulty sustaining attention during lectures, frequent careless errors in schoolwork, failure to finish tasks, chronic disorganization, avoidance of tasks requiring sustained mental effort, misplacing instructional materials, high distractibility by extraneous stimuli, and forgetfulness in daily routines. (Formerly referred to colloquially as ADD).
2. Predominantly Hyperactive-Impulsive Presentation: Characterized by constant fidgeting, tapping hands or feet, leaving seat in classrooms when remaining seated is expected, running or climbing in inappropriate situations, inability to engage in leisure activities quietly, talking excessively, blurting out answers before questions are completed, difficulty awaiting turns, and interrupting or intruding on others.
3. Combined Presentation: Criteria for both inattention and hyperactivity-impulsivity are concurrently met for at least six months. This is the most prevalent presentation in school-age referrals.

Underlying Neuropsychological Mechanism: Executive Functioning Deficits

ADHD is fundamentally a neurobiological impairment of executive functioning regulated by the prefrontal cortex and catecholamine neurotransmitters (dopamine and norepinephrine). Russell Barkley's neuropsychological model identifies the core deficit as impaired behavioral inhibition, which undermines four crucial executive processes:

• Nonverbal Working Memory: Holding sensory events in mind to guide prospective behavior and time perception.
• Internalization of Speech (Verbal Working Memory): Internal self-talk used to direct behavior, follow multi-step mental rules, and regulate problem-solving.
• Self-Regulation of Affect, Motivation, and Arousal: Inhibiting immediate emotional reactions, generating intrinsic motivation for delayed rewards, and sustaining cognitive stamina.
• Reconstitution (Analysis and Synthesis): Breaking down observed behaviors and recombining them into novel, goal-directed action plans.

Medical Diagnosis vs. Educational Eligibility: The Crucial Legal Distinction

A critical concept on the GACE assessment is the distinction between a clinical diagnosis and special education eligibility:

• Medical/Clinical Diagnosis: Rendered by an outside healthcare professional (pediatrician, clinical psychologist, child psychiatrist, or neurologist) under DSM-5 criteria. A clinical diagnosis of ADHD does NOT automatically entitle a student to an IEP under IDEA.
• Educational Eligibility (The "Two-Pronged" Test): An educational multidisciplinary eligibility team must determine that: (1) The student has an impairment meeting the definition of OHI (limited alertness due to ADHD), AND (2) The condition causes an adverse educational impact that necessitates specialized academic instruction.
• Section 504 vs. IDEA: If a student with ADHD exhibits average or above-average academic performance and requires only environmental, organizational, or testing accommodations (such as preferential seating, movement breaks, or extended time) without specialized instruction, the student is served under a Section 504 Accommodation Plan, rather than an IDEA Individualized Education Program (IEP).

Other Chronic and Acute Conditions Under OHI

Special educators must understand the educational implications of other medical conditions classified under OHI:

• Epilepsy (Seizure Disorders): Characterized by recurrent, unprovoked seizures. Includes generalized tonic-clonic seizures (convulsions requiring emergency seizure action plans, recovery positioning, and monitoring) and absence seizures (brief 5-to-15 second lapses of consciousness resembling daydreaming). Teachers must monitor post-ictal cognitive fatigue and side effects of anticonvulsant medications.
• Asthma: Chronic inflammatory disorder of the airways causing wheezing, breathlessness, and coughing. Accommodations include environmental allergen control, inhaler access, and modified physical education participation.
• Type 1 Diabetes Mellitus: Autoimmune destruction of insulin-producing pancreatic cells. Requires Individualized Healthcare Plans (IHPs) accommodating continuous glucose monitoring, scheduled snacks, bathroom access, and emergency recognition of hypoglycemia (tremors, sweating, confusion) vs. hyperglycemia (thirst, lethargy).
• Sickle Cell Anemia: Hereditary blood disorder causing red blood cells to become rigid and sickle-shaped, blocking microcirculation. Results in severe vaso-occlusive pain crises, susceptibility to fatigue, and organ damage. Accommodations require continuous hydration, unrestricted restroom privileges, temperature-controlled classrooms, and generous attendance policies.
• Tourette Syndrome: Neurological disorder characterized by repetitive, involuntary motor and vocal tics (e.g., eye blinking, head jerking, throat clearing, vocalizations). Accommodations include non-punitive classroom environments, private testing rooms, stress reduction, and scheduled sensory breaks to reduce tic suppression fatigue.

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Speech or Language Impairments (SLI): Classifications and Educational Impact

Under IDEA (34 CFR § 300.8(c)(11)), a Speech or Language Impairment is defined as:

"A communication disorder, such as stuttering, impaired articulation, a language impairment, or a voice impairment, that adversely affects a child's educational performance."

Special educators and Speech-Language Pathologists (SLPs) divide communication disorders into two fundamental categories: Speech Disorders (the physical, motor, and acoustic mechanics of sound production) and Language Disorders (the cognitive, symbolic comprehension and formulation of meaning).

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|                  SPEECH DISORDERS vs. LANGUAGE DISORDERS CLASSIFICATION                 |
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|  SPEECH DISORDERS (Motor & Acoustic Production)                                         |
|  - Articulation Disorders: Motor production errors (SODA: Substitutions, Omissions,     |
|    Distortions, Additions; e.g., saying "wabbit" for "rabbit").                         |
|  - Phonological Disorders: Rule-based linguistic errors in sound systems (e.g., fronting|
|    "car" to "tar", cluster reduction "play" to "pay").                                 |
|  - Fluency Disorders: Disruptions in the flow and rhythm of speech (stuttering, sound   |
|    prolongations, syllable repetitions, postural blocks, secondary struggle tension).   |
|  - Voice Disorders: Abnormal pitch, loudness, resonance, or vocal quality (chronic      |
|    hoarseness, vocal nodules, hypernasality, hyponasality).                              |
|                                                                                         |
|  LANGUAGE DISORDERS (Cognitive & Linguistic Processing)                                 |
|  - Receptive Language: Impaired ability to comprehend, process, and integrate incoming  |
|    verbal or written symbols (difficulty following multi-step commands, decoding text). |
|  - Expressive Language: Impaired ability to encode and formulate thoughts into words,   |
|    grammatical structures, and narratives (limited vocabulary, syntactic errors).       |
|  - Pragmatic Language: Impaired social use of language (conversational turn-taking,    |
|    interpreting figurative language/idioms, adjusting tone to social context).          |
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Collaborative Service Delivery with Speech-Language Pathologists (SLPs)

Special educators work closely with SLPs in both integrated co-teaching (push-in) and direct clinical (pull-out) formats. In the general curriculum, communication disorders directly undermine reading comprehension, written expression, oral presentations, and social collaboration. Evidence-based accommodations include providing visual graphic organizers, pairing oral directions with written text, using Augmentative and Alternative Communication (AAC) systems (ranging from low-tech communication boards to high-tech speech-generating devices with dynamic eye-gaze tracking), pre-teaching technical vocabulary, and ensuring adequate response latency (wait time) during oral questioning.

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High-Incidence Disabilities Comparison Matrix

The following synthesis details the legal classifications, hallmark features, cognitive profiles, and high-leverage accommodations across high-incidence categories: