Validity of alternative approaches for the identification of learning disabilities: operationalizing unexpected underachievement.

This article reviews the validity of models based on (a) aptitude-achievement discrepancies, (b) low achievement, (c) intraindividual differences, and (d) response to instruction for the classification and identification of learning disabilities (LD). Models based on aptitude-achievement discrepancies and intraindividual differences showed little evidence of discriminant validity. Low achievement models had stronger discriminant validity but do not adequately assess the most significant component of the LD construct, unexpected underachievement. All three of these status models have limited reliability because of their reliance on a measurement at a single time point. Models that incorporate response to instruction have stronger reliability and validity but cannot represent the sole criterion for LD identification. Hybrid models combining low achievement and response to instruction most clearly capture the LD construct and have the most direct relation to instruction. The assessment of students for LD must reflect a stronger underlying classification that takes into account relations with other developmental disorders as well as the reliability and validity of the underlying classification and resultant identification system.