ABSTRACT
The concept of a learning disability is rooted in the premise that neurological anomalies can cause uneven development of cognitive capabilities. The resulting pattern of strengths and weaknesses is captured in an operational definition. The modal version of the definition is a significant discrepancy between ability and achievement. Despite widespread use of this definition, its adequacy has been questioned. We argue that a satisfactory operational definition must meet three criteria. The first two criteria are customary for any definition in science: validity and reliability. The third criterion is unique to the learning disability (LD) initiative—the definition must meet the letter and spirit of special education laws. Kavale’s review of nearly 40 years of legislation and research (Kavale, this volume) supports the idea that a version of an IQ-achievement discrepancy definition can be statistically reliable (e.g., Kavale, Fuchs, & Scruggs, 1994) but the review fails to establish that the other two criteria have been satisfied.
