Given the importance of math in today's society, it is critical that children who are at risk for math difficulty are identified early. We developed and validated a prekindergarten math subtest (i.e., CIRCLE Progress Monitoring [CPM] Math Subtest). This teacher-completed measure evaluates domains considered important for later math development. Evaluation of validity was undertaken in a longitudinal sample of 383 children (M[subscript age] = 4.9 years), and a follow-up sample of 3,691 children (M[subscript age] = 4.4 years). The measure demonstrated adequate psychometric properties, including strong internal consistency reliability ([alpha] = 0.94) and test-retest reliability (r = 0.78). Evaluation of concurrent and predictive validity demonstrated scores on the CPM Math Subtest were correlated with scores on other assessments at high levels (rs from 0.55-0.65). Exploratory and confirmatory factor analyses revealed that the subtest conforms to a well-defined five-factor model that parallels areas considered to be important in the math literature.