This article presents findings from the first independent, third-party appraisal of the impact of the Teacher Advancement Program (TAP) on student test score gains in mathematics. TAP is a comprehensive school reform model designed to attract highly effective teachers, improve instructional effectiveness, and elevate student achievement. We use a panel data set to estimate a TAP treatment effect by comparing student test score gains in mathematics in schools that participated in TAP with student test score gains in non-TAP schools. Ordinary least squares estimation reveals a positive TAP treatment effect on student test score gains in the elementary grades, with weaker but still positive point estimates in the secondary grades. When estimation methods control for selection bias, the positive effect remains at the elementary level, but most estimates for grades 6 through 10 turn negative. Our findings are qualified by the lack of information on the fidelity of implementation across TAP schools and on variation in features of TAP programs at the school level.