This study examined longitudinal predictive relationships between young children's classroom behaviors and their growth in mathematics skills during the primary grades. Using the Early Childhood Longitudinal Study--Kindergarten cohort, the authors tested a longitudinal model featuring positive (interpersonal skills and approaches to learning) and negative (internalizing and externalizing) behaviors at kindergarten entry as predictors of growth in mathematics achievement through 3rd grade. Results indicated that negative behaviors demonstrate negligible relationships with early development of mathematics skills. Interpersonal skills demonstrated a small negative relationship with mathematics growth when other positive behaviors were included as predictors in the model. In contrast, approaches to learning (goal-directed behavior, persistence, organization) demonstrated small positive relationships with growth in mathematical skills and may represent a skill domain for educators to consider in designing their instructional practices.