An examination of an implementation of the simple difference score distribution model in learning disability identification

An important part of the PL 94–142 learning disability (LD) definition is the requirement that a child manifest a discrepancy between ability and achievement to be eligible for special education services. Because the language used in PL 94–142 is generic, it has been left to each state to determine how this discrepancy criterion is to be implemented. Subsequently, numerous discrepancy formulas have been proposed, and many of them have been rejected as statistically unsound. In response to this professional paralysis, and faced with continued increasing LD enrollment, the California State Legislature took matters into its own hands and passed legislation mandating the use of the simple difference score distribution model as part of the state LD eligibility criteria. This study examines the implementation of this procedure in six California school districts. The results revealed that the IEP teams' placement decisions were influenced by the students' discrepancy scores, but that prereferral status (initial evaluation vs. reevaluation) was a better predictor of postevaluation special education status. Shortcomings of this discrepancy procedure and implications for the IEP team decisionmaking process are discussed.