This meta-analysis reviews research on the achievement effects of comprehensive school reform (CSR) and summarizes the specific effects of 29 widely implemented models. There are limitations on the overall quantity and quality of the research base, but the overall effects of CSR appear promising. The combined quantity, quality, and statistical significance of evidence from three models, in particular, set them apart. Whether evaluations are conducted by developers or by third-party evaluators and whether evaluators use one-group pre-post designs or control groups are important factors for understanding differences in CSR effects. Schools that implemented CSR models for 5 years or more showed particularly strong effects, and the benefits were consistent across schools of varying poverty levels. A long-term commitment to research-proven educational reform is needed to establish a strong marketplace of scientifically based CSR models.