The PD program evaluated in this study is designed to address the problem of low student achievement in topics in rational numbers. The study focuses on seventh grade, the culminating year for teaching those topics. The study randomly assigned 77 mid- and high-poverty schools from 12 districts to treatment and control conditions and collected outcome data on teachers and students. [For the accompanying papers, see Paper #2 (ED512820) and Paper #3 (ED512821).]