This study was the first randomized controlled trial to assess the impact of Odyssey Math on student achievement. The study had the statistical power needed to detect a 0.20 effect size and was well designed in that comparable groups were created at baseline and maintained through posttesting. Implementation during the school year was documented and shown to be consistent with typical implementation of the Odyssey Math software. The results from the multilevel model with pretest covariates also indicate that Odyssey Math did not yield a statistically significant impact on end-of-year student achievement. This study generated a statistically unbiased estimate of the effect of Odyssey Math on student achievement when implemented in typical school settings with typical teacher and student use. However, the findings apply only to participating schools, teachers, and students because the study used a volunteer sample.