Understanding Specific Learning Differences: Definitions, Characteristics, and Implications
Specific Learning Disabilities (SLDs), often referred to as learning disabilities (LD), encompass a range of brain-based disorders that impact an individual's ability to excel in specific academic domains. These disabilities manifest uniquely in each individual, but their primary impact is on skills related to reading, writing, and mathematics. Understanding the complexities of SLDs is crucial for effective identification, intervention, and support for affected individuals.
Defining Specific Learning Disabilities
A specific learning disability is characterized as a disorder affecting one or more of the fundamental learning processes involved in comprehending or utilizing language, whether spoken or written. This can manifest as significant difficulties in listening, speaking, reading, writing, spelling, or performing mathematical tasks. Conditions such as dyslexia, dyscalculia, dysgraphia, or developmental aphasia may be associated with SLDs.
It is important to note that a specific learning disability does not encompass learning problems that primarily arise from visual, hearing, motor, intellectual, or emotional/behavioral disabilities, limited English proficiency, or environmental, cultural, or economic factors.
Historical Context and Evolution of the SLD Definition
Fifty years ago, the US federal government recognized specific learning disabilities (SLD) as a potentially disabling condition that interferes with adaptation at school and in society. Over these 50 years, a significant research base has emerged on the identification and treatment of SLD, with greater understanding of the cognitive, neurobiological, and environmental causes of these disorders. The original 1968 definition of SLD remains statutory through different reauthorizations of the 1975 special education legislation that provided free and appropriate public education for all children with disabilities, now referred to as the Individuals with Disabilities Education Act (IDEA, 2004).
The Individuals with Disabilities Education Act (IDEA), enacted in 1975 as Public Law 94-142, mandates that children and youth ages 3-21 with disabilities be provided a free and appropriate public school education in the least restricted environment.
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Three strands of phenomenological inquiry culminated in the 1968 definition and have continued to shape current terminology and conventions in the field of SLD. The first, a medical strand, originated in 1676, when Johannes Schmidt described an adult who had lost his ability to read (but with preserved ability to write and spell) because of a stroke. Interest in this strand reemerged in the 1870s with the publication of a string of adult cases who had lived through a stroke or traumatic brain injury. Subsequent cases involved children who were unable to learn to read despite success in mathematics and an absence of brain injury, which was termed “word blindness” (W. P. Morgan, 1896).
The second strand is directly related to the formalization of the American Psychiatric Association’s Diagnostic and Statistical Manual (DSM). Rooted in the work of biologically oriented physicians, the 1952 first edition (DSM-I) referenced a category of chronic brain syndromes of unknown cause that focused largely on behavioral presentations we now recognize as hyperkinesis and Attention Deficit Hyperactivity Disorder (ADHD).
The third strand originated from the development of effective interventions based on cognitive and linguistic models of observed academic difficulties. This strand, endorsed in the 1960s by Samuel Kirk and associates, viewed SLD as an overarching category of spoken and written language difficulties that manifested as disabilities in reading (dyslexia), mathematics (dyscalculia), and writing (dysgraphia).
Common Types of Specific Learning Disabilities
Several distinct types of SLDs have been identified, each affecting specific academic skills:
Dyslexia: Reading Difficulties
Dyslexia is a well-known learning disability that primarily impacts reading. People with dyslexia struggle to recognize and blend sounds in words, read fluently, and spell accurately. SWRD represents difficulties with beginning reading skills due at least in part to phonological processing deficits, while other language indicators (e.g., vocabulary) may be preserved (Pennington, 2009). In contrast, SRCD (Cutting et al., 2013), which is more apparent later in development, is associated with non-phonological language weaknesses (Scarborough, 2005).
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Dysgraphia: Writing Challenges
Dysgraphia is a learning disability associated with writing. Individuals with dysgraphia may make grammar and spelling mistakes, produce writing that lacks structure and clarity, and find it challenging to form letters neatly. Specific written expression disability, SWED (Berninger, 2004; Graham, Collins, & Rigby-Wills, 2017) occurs in the mechanical act of writing (i.e., handwriting, keyboarding, spelling), associated with fine motor-perceptual skills, or in composing text (i.e., planning and revising, understanding genre), associated with oral language skills, executive functions, and the automaticity of transcription skills.
Dyscalculia: Mathematical Struggles
Dyscalculia is a learning disability that affects an individual’s mathematical skills. Math SLDs are differentiated as calculations (SMD) versus problem solving (word problems) SLD, which are associated with distinct cognitive deficits (L. S. Fuchs et al., 2010) and require different forms of intervention (L. S. Fuchs et al., 2014). Calculation is more linked to attention and phonological processing, while problem solving is more linked to language comprehension and reasoning; working memory has been associated with both.
Identification and Assessment of SLDs
Children are identified as SLD through IDEA when a child does not meet state-approved age- or grade-level standards in one or more of the following areas: oral expression, listening comprehension, written expression, basic reading skills, reading fluency, reading comprehension, mathematics calculation, and mathematics problem solving.
Identification methods have searched for other markers of unexpected underachievement beyond low achievement, but always include exclusionary factors. Diagnosis solely by exclusion has been criticized due to the heterogeneity of the resultant groups (Rutter, 1982); thus, the introduction of a discrepancy paradigm. One approach relies on the aptitude-achievement discrepancy, commonly operationalized as a discrepancy between measures of IQ and achievement in a specific academic domain.
Although its exclusionary criteria were well specified, the definition of SLD did not provide clear inclusionary criteria. Thus, the US Department of Education’s 1977 regulatory definition of SLD included a cognitive discrepancy between higher IQ and lower achievement as an inclusionary criterion. This discrepancy was viewed as a marker for unexpected underachievement and penetrated the policy and practice of SLD in the US and abroad. In many settings, the measurement of such a discrepancy is still considered key to identification. Yet, IDEA 2004 and the DSM-5 moved away from this requirement due to a lack of evidence that SLD varies with IQ and numerous philosophical and technical challenges to the notion of discrepancy (Fletcher, Lyon, Fuchs, & Barnes, 2019).
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Response to Intervention (RTI)
Second, IDEA indicates that, when determining whether a child has a specific learning disability, a n LEA may use a process that determines if a child responds to scientific, research-based intervention as a part of the evaluation procedures used to determine if the child has a disability. A RTI model would be designed to ensure that children who are indicating a likelihood of failing in the early grades and being identified as having a specific learning disability receive scientific, research-based intervention as soon as possible. The eligibility for special education services would focus on the children who, even with these services, are not able to be successful. The focus of RTI is on responding to the instructional challenges caused by the suspected disability, not on giving tests to document the failure of the student.
Prevalence and Demographic Considerations
SLD, exemplified here by Specific Word Reading, Reading Comprehension, Mathematics, and Written Expression Disabilities, represent spectrum disorders each occurring in approximately 5-15% of the school-aged population.
The percentage of children served by federally mandated special education programs, out of total public school enrollment, increased from 8.3 percent to 13.8 percent between 1976-77 and 2004-05. Much of this overall increase can be attributed to a rise in the percentage of students identified as having SLD from 1976-77 (1.8 percent) to 2004-05 (5.7 percent). The overall percentage of students being served in programs for those with disabilities decreased between 2004-05 (13.8 percent) and 2013-14 (12.9 percent). The percentage of children identified with SLD declined from 5.7 percent to 4.5 percent of the total public school enrollment during this period.
Cognitive and Neurological Basis of SLDs
A rich literature on cognitive models of SLD (Elliott & Grigorenko, 2014; Fletcher et al., 2019) provides the basis for five central ideas. First, SLD are componential (Melby-Lervåg, Lyster, & Hulme, 2012; Peng & Fuchs, 2016): Their academic manifestations arise on a landscape of peaks, valleys, and canyons in various cognitive processes, such that individuals with SLD have weaknesses in specific processes, rather than global intellectual disability (Morris et al., 1998). Second, the cognitive components associated with SLD, just like academic skills and instructional response, are dimensional and normally distributed in the general population (Ellis, 1984), such that understanding typical acquisition should provide insight into SLD and vice versa (Rayner, Foorman, Perfetti, Pesetsky, & Seidenberg, 2001). Third, each academic and cognitive component may have a distinct signature in the brain and genome. These signatures and etiologies likely overlap because they are correlated, but are not interchangeable, as their unique features substantiate the distinctness of various SLD (Vandermosten, Hoeft, & Norton, 2016). Fourth, the overlap at least partially explains their rates of comorbidity (Berninger & Abbott, 2010; Szucs, 2016; Willcutt et al., 2013).
Rights and Support for Individuals with SLDs
Parents/caregivers of children, students, and young adults with learning disabilities should know their rights. IDEA mandates that children and youth ages 3-21 with disabilities be provided a free and appropriate public school education in the least restricted environment.
Long-Term Outcomes and Implications
In addition to risk for academic deficiencies and related functional social, emotional, and behavioral difficulties, those with SLD often have poorer long-term social and vocational outcomes.
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