ABSTRACT
Most definitions of dyslexia involve the assessment of a discrepancy between reading ability and measured intelligence. These discrepancy definitions carry the implicit assumption that the reading difficulties of the dyslexic stem from problems different from those characterizing the poor reader without IQ discrepancy. An accumulating body of empirical evidence appears to contradict this assumption. The phenotypic performance profile that defines reading disability does not seem to differ for reading-disabled children with or without aptitude/achievement discrepancies. Degree of aptitude/achievement discrepancy is unrelated to the unique cognitive tradeoffs that are characteristic of the word identification performance of reading-disabled children. Genetic studies have indicated that IQ-discrepancy measurement does not identify a group of children with significantly different heritability values for core information processing deficits. Finally, there are as yet no indications that the neuroanatomical anomalies that are associated with reading disability are more characteristic of high-IQ than of low-IQ poor readers. These findings are extremely problematic for traditional conceptions of reading disability that rely on aptitude/achievement discrepancy to define a group of children whose reading problems are cognitively, physiologically, and etiologically distinctive.
