This study details the construction of parameters for generating subskill mastery math measures to be used for screening, intervention planning, progress monitoring, and proximal program evaluation. Parameters for generating assessment measures were built and tested to verify initial equivalence of generated measures using potential digits correct as a proxy for task difficulty across generated measures. Generated measures met initial equivalence criteria and were subjected to further reliability analysis. Measures were generated and administered 1 week apart at fall and winter to students in Grades K, 1, 3, 5, and 7. Thirty-four screening measures were examined for delayed alternate form reliability, risk decision agreement, and interobserver agreement. Delayed alternate form reliability values generally exceeded r = 0.80, could be reliably scored, and yielded consistent risk decisions. Future research directions were discussed.