This article investigates the effect of private lower secondary schools on student achievement in France. I use propensity score matching on a large French database to estimate the effect of enrollment in a private school on academic achievement as measured by ninth-grade test scores in three school subjects. I find that private school attendance has a large and significant effect on educational success. Boys' (girls') scores in private school were between 0.193 (0.138) and 0.222 (0.198) standard deviations higher on standardized tests in ninth grade. A series of checks confirm the robustness of these results.