Ability—Achievement Discrepancy, Response to Intervention, and Assessment of Cognitive Abilities/Processes in Specific Learning Disability Identification: Toward a Contemporary Operational Definition

Abstract

The category of specific learning disability (SLD) remains the largest and most contentious area of special education. A primary problem is overidentification of students with SLD as evidenced by the SLD category representing approximately 5% of the school population and 50% of the special education population. Partially responsible for this problem is the overreliance on the ability–achievement discrepancy criterion as the sole indicator of SLD, a practice that remains widespread. Recently, new ways to conceptualize and define SLD have been proposed in an attempt to remedy the overidentification problem (e.g., Fletcher, Coulter, Reschly, & Vaughn, 2004). Most popular is a model that conceptualizes SLD in terms of a failure to respond to intervention (RTI) (Berninger & Abbott, 1994). The purpose of this chapter is to briefly review these two methods of SLD identification, the ability–achievement discrepancy criterion and RTI. It is our belief that neither of these methods, when used as the sole indicator of SLD, can identify this condition reliably and validly. This is because SLD may be present in students with and without a significant ability–achievement discrepancy (see Aaron (1997) for a comprehensive review) and in students who fail to respond and who do respond favorably to scientifically based interventions. We believe the missing component in both of these SLD methods is information on the student’s functioning across a broad range of cognitive abilities and processes, particularly those that explain significant variance in academic achievement. Indeed, the federal definition of SLD is “a disorder in one or more of the basic psychological processes. . . ” (Individuals with Disabilities Education Act [IDEA] 2004). Therefore, this chapter discusses evaluation of cognitive abilities/processes as defined by contemporary Cattell– Horn–Carroll (CHC) theory and its research base. Inherent in this discussion is a summary of the research on the relations between cognitive abilities/processes and academic achievement, information we believe is necessary to (a) determine whether a processing deficit(s) is the probable cause of a student’s academic difficulties and (b) restructure and redirect interventions for nonresponders in an RTI model. Keogh (2005) discussed criteria for determining the adequacy and utility of a diagnostic system, such as the ability–achievement discrepancy and RTI models. The criteria include homogeneity (Do category members resemble one another?), reliability (Is there agreement about who should be included in the category?), and validity (Does category membership provide consistent information?). Keogh (2005, p. 101) suggested that, SLD “is real and that it describes problems that are distinct from