A study was designed to assess the effects of the introduction of a state-mandated minimum competency test (MCT) on students' acquisition of basic and high-level mathematics skills. Subjects of the study were ninth-grade students, all of whom attended the same schools in the Austin (Texas) Independent School District, and took the same form of the standardized achievement test 1 year before, 1 year after, and 3 years after the introduction of the MCT. Items on the mathematics subtest of the Sequential Tests of Educational Progress (STEP) were divided into Basic Skills, and High-level Skills. Subjects' overall eighth-grade averages, as a measure of previous achievement, were used as the covariate in the study. Results of the data analyses indicate that the Basic Skills mean increased significantly between 1979 and 1981 but did not change significantly thereafter. The observed increase was constant for students at all levels of achievement. Analyses of High-level Skills means indicate that there was a significant interaction with level of achievement. Low achievers demonstrated a significant increase, and high achievers demonstrated a significant decline in High-level Skills scores between 1979 and 1983. Implications of the findings and limitations on the conclusions are discussed. (Author/JAZ)