Why Scientific Research must Guide Educational Policy and Instructional Practices in Learning Disabilities

Abstract

SOME BACKGROUND When I initiated my research program in the neuropsychology of learning disabilities (LDs) in 1974, I was guided in part by the scholarship of William Cruickshank, Helmer Myklebust, Doris Johnson, and Samuel Kirk, among others. These gifted pioneers made an indelible impact on my thinking and my research over the years. I found compelling their clinical insights about children who had significant reading problems (and other academic problems) despite robust intellectual capability, since I worked with many such children as a psychologist in the public schools. I also learned a great deal from them about the instructional skills that teachers must possess in order to address individual differences in learning. I was particularly fascinated by this concept of unexpected underachievement and the paradox of learning difficulties in an intellectually competent student. Misguided Assumptions As I became interested in this concept of unexpected underachievement, I was struck by the heterogeneity of reading difficulties that I observed in schools. When I began my research career, I focused on this heterogeneity and asked whether children identified with LDs in reading could be assigned to more homogeneous subtypes, with each subtype described by different reading-related deficits. My goal, if I found subtypes, was to then identify and validate subtype-by-treatment interactions. Unfortunately, my search for valid subtypes and interactions with different treatments was unsuccessful for several reasons. Fundamentally, my work was based on scientifically untested assumptions underlying the construct of LDs: I assumed that the definition of LDs at that time was valid and I assumed that LDs was a distinct category of disability that could be differentiated empirically from other categories through psychometric (e.g., IQ-achievement discrepancies) and exclusionary criteria. I was wrong on both counts, but I figured I might not be alone in making these assumptions. At the same time, it was clear to me that the field had made significant contributions by bringing special education services to students with LDs--services that had previously been denied. By 1969, parental and professional advocacy resulted in federal recognition of LDs and access to due process to ensure a free and appropriate public education. However, it troubled me that federal policy may have been based on the same flawed assumptions that I had made. While I did not have any doubts that LDs constituted a genuine category of exceptionality, I came to realize that the definition of LDs, instantiated in federal legislation, was based upon clinical observations and anecdotal evidence rather than replicated scientific evidence. Lessons Learned To make myself feel better I could make the excuse that my faulty assumptions were based on the knowledge of LDs available at the time. But that doesn't cut it. In hindsight, I should have broadened my view of LDs beyond the literature specific to the field and my training (experimental and physiological psychology, learning disabilities), and turned to the literatures in the developmental, cognitive, linguistic, psychometric and classification sciences as well. When I eventually did examine these sources in depth, I learned a great deal about individual differences, principles of classification, continuous distributions, the vagaries of establishing cut points along the normal distribution, and the fact that there were significant problems with the notion that IQ scores are valid predictors of learning potential. I learned that a comparison of IQ scores with achievement scores to derive a discrepancy as a marker for LDs is fraught with psychometric, statistical, and conceptual problems that render the putative relationship between the scores unreliable and meaningless (see Steubing et al., 2002, for a review of these issues). In addition, I learned that using a discrepancy metric in the identification of LDs may harm children more than it helps, not only because criteria are inconsistent across states and schools, but also because a discrepancy typically requires failure to occur (i. …