The Neuropsychology of Reading Disorders
Before we discuss specific types of learning disorders (LDs), we begin this chapter with a historical overview of the field of learning disability research and practice. We distinguish between “LDs,” a clinical label, and “learning disabilities,” a legal label. As we review the history of learning disabilities, keep this distinction in mind; it may be related to controversy regarding learning disability identification and intervention practices. Nearly half of the children served by the Individuals with Disabilities Education Act (IDEA) are children with learning disabilities (National Center for Education Statistics, 1999), but we are still debating what learning disabilities are, how we assess them, and how best to determine eligibility for learning disability services (Kaufman & Kaufman, 2001). Although most educators and researchers now recognize that children with learning disabilities are a heterogeneous population, few have attempted to examine this diversity until recently. There is still no clear agreement on the etiology of learning disabilities. Various researchers and practitioners advocate conceptualizing learning disabilities as developmental delays, developmental deficits, or environmental problems. Researchers are certainly concerned about the diagnostic validity of learning disabilities, but there is even more concern about learning disability identification in the schools (e.g., Lyon et al., 2001; MacMillan, Gresham, & Bocian, 1998; B. A. Shaywitz, Fletcher, Holahan, & Shaywitz, 1992). In addition, most researchers and clinicians still operate under the assumption that there are verbal and nonverbal subtypes of learning disabilities—a conceptualization first described over three decades ago (Johnson & Myklebust, 1967), which confounds diagnostic accuracy and intervention efficacy.
With no clear consensus on the cause of learning disabilities, could psychologists have obscured important differences among these different types of learning problems? Should children with developmental deficits be the only ones classified with learning disabilities? Isn't it better to think of learning disabilities as developmental delays? The short answer is that for children with “true” learning disabilities, longitudinal research confirms that the delay model is inadequate for explaining the nature of their specific deficits (Francis, Shaywitz, Stuebing, Shaywitz, & Fletcher, 1994).