The reliability and validity of 4 approaches to the assessment of children and adolescents with learning disabilities (LD) are reviewed, including models based on (a) aptitude-achievement discrepancies, (b) low achievement, (c) intra-individual differences, and (d) response to intervention (RTI). We identify serious psychometric problems that affect the reliability of models based on aptitude-achievement discrepancies and low achievement. There are also significant validity problems for models based on aptitude-achievement discrepancies and intra-individual differences. Models that incorporate RTI have considerable potential for addressing both the reliability and validity issues but cannot represent the sole criterion for LD identification. We suggest that models incorporating both low achievement and RTI concepts have the strongest evidence base and the most direct relation to treatment. The assessment of children for LD must reflect a stronger underlying classification that takes into account relations with other childhood disorders as well as the reliability and validity of the underlying classification and resultant assessment and identification system. The implications of this type of model for clinical assessments of children for whom LD is a concern are discussed.