The purpose of this study was to examine technical and instructional features of a kindergarten curriculum-based measurement (CBM) tool designed to track students' mathematics progress in terms of computational concepts, procedures, and counting strategies. Students in 10 kindergarten classrooms in three elementary schools completed alternate forms of the CBM measure twice per month from January to May. Mathematics development was indexed on a standardized mathematics achievement test in May. Findings indicate strong reliability and validity of the CBM system, with coefficients exceeding 0.80 and 0.60, respectively. Technical features of the CBM system's skills analysis suggest implications for teachers' instructional decision-making. (Contains 3 figures and 2 tables.) [Additional financial support for this research was provided by the Eunice Kennedy Shriver National Institute of Child Health & Human Development grant to Vanderbilt University.]