Concern about poor mathematics achievement in U.S. schools has increased in recent years. In part, poor achievement may be attributed to a lack of attention to early instruction and missed opportunities to build on young children's early understanding of mathematics. This study examined the development and feasibility testing of a kindergarten mathematics curriculum designed to focus on the development of early number sense, geometry, measurement, and mathematics vocabulary. A mixed-model analysis of covariance, using pretest score as a covariate, was used to determine the effect of the experimental curriculum on student achievement on a standardized measure of early mathematics. Achievement results as well as implementation fidelity and teacher satisfaction suggest that further empirical research on the efficacy of the curriculum is warranted. (Contains 1 table.)