Concerns about the ability-achievement discrepancy method for specific learning disability (SLD) determination led to alternative research-based methods, such as failure to respond to intervention. Neither of these "regulatory" methods address the "statutory" SLD definition, which explicitly includes a deficit in "basic psychological processes". Examining neuropsychological processing differences among typical children and children with math SLD, commonality analyses revealed that "Differential Ability Scales--Second Edition" (DAS-II) predictors accounted for more achievement variance in typical children (46% to 58%) than in children with math SLD (33% to 50%), with substantial loss of predictive validity when General Conceptual Ability was used instead of subcomponent scores. Results suggest that differences in typical predictor-outcome relationships may provide a foundation for developing specific cognitive and academic interventions for children with math SLD. (Contains 6 tables.)