The positive impact of Science, Technology, Engineering, and Mathematics (STEM) programs on student achievement, attitude, interest, communication skills and problem-solving has alerted the education community to reform instructional approaches in STEM subjects. This meta-analysis study aims to analyze previous studies' results of STEM program impacting students' mathematics achievement. The criteria for inclusion of literature in the meta-analysis were: published between 1998 and 2017, employed experimental research design, and reported data necessary for computing effect sizes. Based on the Hedges-g effect size values, three of the studies were categorized into the large effect category (n=3), two studies were classified under the medium effect group (n=2), and twelve studies were considered to be small effect sizes (n=12). The overall weighted average effect size was 0.242 with a corresponding p-value of 0.023 demonstrating that STEM had an impact on student mathematics achievement. However, no evidence was found concerning the impact of STEM program on students' mathematics achievement based on the three moderator variables: education level, publication source, and length of intervention. Limitations and implications of the study were discussed.