July 2019: Specific Learning Disabilities: 50 years of Science and Practice

Overview

Fifty years ago, the U.S. federal government recognized specific learning disabilities (SLDs) as a potentially disabling condition that interferes with successful performance in academic settings and society (United States Office of Education, 1968). A child is at-risk for SLD when they fail to meet state grade- or age-level standards in one or more of the following areas: oral expression, listening comprehension, written expression, basic reading skills, reading fluency, reading comprehension, mathematics calculations, and mathematics problem solving. On average, students identified as having SLD represent roughly 50% of all children served under Individuals with a Disability Education Act (IDEA) aged 3–21. Over the last half century, our understanding of SLD has grown substantially due in part to significant investments by the National Institute of Child Health and Human Development (NICHD).

To mark the 50th anniversary of the U.S. federal government recognizing specific learning disabilities (SLD), a team of learning disability experts funded by NICHD led by Elena Grigorenko reviewed historical and current trends in research and practice to describe the present knowledge base on SLD and identify important areas for future research. The authors reviewed related research across the fields of psychology, education, genetics, and cognitive neuroscience to address questions related to the causes and symptoms of SLD as well as the best ways to identify and treat students with SLD.

What research has influenced understanding of SLDs?

Three historical strands shaped the original conception of SLD and continue to inform our current understanding of SLD.

1. One line of research, the medical strand, primarily studied learning difficulties in adults who had experienced a stroke or traumatic brain injury. Over time, this research focused on learning difficulties that occurred in the absence of a brain injury and were both specific (i.e., related to specific academic skills) and unexpected (i.e., present despite average intelligence, motivation, and opportunity).
2. The biological strand initially thought learning difficulties resulted from “mild brain damage;” however, over time, researchers determined these students had “minimal brain dysfunction” and “near, average, or above average intelligence with certain learning or behavioral disabilities…associated with deviations of function of the central nervous system” (Clements, 1966, pp. 9–10).
3. The final strand regarded SLD as a category of spoken and written language difficulties manifested in reading (dyslexia), mathematics (dyscalculia), and writing (dysgraphia). Research in this strand by Samuel Kirk and colleagues played a key role in the development of research in this area and was instrumental to the definition of SLD adopted in 1968.

What is the definition of SLD?

Grigorenko and colleagues review how the definition of SLD has evolved over time and how SLD is defined by law (e.g., Individuals with Disabilities Act, 2004) and diagnostic criteria (e.g., Diagnostic and Statistical Manual-5; American Psychiatric Association, 2013). The authors note that SLD is widely recognized as a heterogenous set of academic skill disorders that can occur in word reading, reading comprehension, math calculation, math word problems, and writing. Based on cognitive research, the authors presented five central ideas about SLD that help to characterize the disorder:

1. SLD is componential, which means each child has specific areas of underperformance as opposed to a global intellectual disability.
2. Cognitive components are dimensional and normally distributed in the general population. In other words, students identified with SLD will vary in the severity of their difficulties and may be very similar to students who demonstrate academic underperformance but were not identified with a SLD.
3. Each academic and cognitive component may have a distinct signature on in the brain.
4. Overlap in these neural signatures partially explain the high rates of comorbidity.
5. These deficiencies will continue through life without appropriate intervention.

What is the best method of identifying SLD?

To be identified with SLD, there is general agreement that a student must display unexpected underachievement, yet there is not widespread agreement about how unexpectedness is operationalized. Approaches to identification currently under consideration and in use in schools include identifying students based on (a) a discrepancy between achievement and IQ, (b) uneven patterns of strengths and weaknesses profiles of cognitive functioning (e.g., students demonstrate poor phonological processing deficits and advanced visual-spatial skills), and (c) evidence of persisting difficulties despite appropriate intervention. The authors indicate the former two approaches to SLD identification that are not well supported by empirical research. The latter method of SLD identification is typically operationalized in schools through response to intervention (RTI) or multi-tiered system of supports (MTSS). These multi-tiered systems identify students for SLD based on inadequate response to classroom instruction (Tier 1) and supplemental interventions (Tier 2). Although not without concerns, Grigorenko and colleagues identify a couple of important advantages to this approach: Tier 1 supports the implementation of intervention prior to the determination of SLD eligibility, and Tier 2 encourages schools to screen for early indicators of academic problems and then collect data on an ongoing basis to monitor students at-risk for SLD. (For information about best practices in identifying students with SLD, please see this practice guide developed by Drs. Jack Fletcher and Jeremy Miciak.)

How has neurobiological research influenced our understanding of SLD?

Neuroimaging studies have shown differences in activation of functional patterns between typically developing children and students with specific word reading disabilities (SWRD). These findings indicate atypicalities in the gray matter structures associated with reading and their connecting pathways. Evidence shows these atypicalities can be normalized with successful intervention. Studies of the familial nature of SLD have found that 30–80% of variance in reading, math, or spelling outcomes can be explained by heritable factors, such as having one or multiple family members with SWRD.

Implication for Practitioners

For psychologists and instructional school staff focused on the identification of SLD, it is important to recognize that the scientific evidence base provides support for using specific approaches to the identification of and treatment of SLD. It is critical that evaluations and assessments

• be timely and make use of multiple, technically sound measures for identification decisions;
• take into consideration comorbidities and other contextual factors;
• collect data on an ongoing basis in the context of intervention efforts to support the students; and
• be used to inform instruction.

Intervention instruction should target the specific needs of students (i.e., reading, writing, and/or math) and adhere to the following research-validated instructional principles for students with SLD:

• Explicit: New information is clearly presented, models skills and strategies, provide lots of opportunities for guided practice until students show mastery during independent practice.
• Individualized: Instruction is aligned to students’ specific needs based on ongoing data collection.
• Comprehensive: Instruction addresses the varied needs of students, including multiple academic domain deficits and other related difficulties such as students’ inattention and anxiety.
• Adjusts intensity: Dimensions of intensity (e.g., dosage, group size, number of practice opportunities) are adjusted based on student need.
• Occurs early in development: Results from studies for students with reading difficulties have shown that students are more responsive in the early grades (K–2) than later grades.
• Directly target academic skills: Instruction should primarily target the specific academic skill deficits of students with SLD, as interventions that do not involve teaching academic skills—such as cognitive working memory trainings or physical exercise trainings—have been found to be ineffective.

Conclusion

This paper highlights the tremendous progress made in the scientific understanding of SLD that has occurred due to interdisciplinary research. This research provides several important findings. For school-based practitioners, two of the most important findings may be (1) assessments should be timely to avoid delays in instruction and be conducted in the context of previous instructional efforts, as is typically done in RTI/MTSS approaches, (2) assessment data should be used to inform instruction and ensure that intervention programs are evidence-based and reflect general principals of effective intervention (i.e., explicit, comprehensive, individualized, and intensive). Despite these advancements in science and practice, the authors contend research is still urgently needed to understand individual differences in development and response to instruction based on data from multiple scientific domains, including neurological, genetic, cognitive, and environmental, to better identify and instruct children with SLD.