The study reviewed in this paper examined the effects of "mastery learning" and "student team learning" on the math achievement of high school students. The analysis included 588 ninth-grade students in 16 urban Philadelphia high schools. The study assessed the effectiveness of the different conditions after one year by comparing student performance on a shortened version of the Comprehensive Test of Basic Skills (CTBS), Mathematics Computations and Concepts and Applications subscales. The study found, and the What Works Clearinghouse (WWC) confirmed, a statistically significant positive effect on math achievement for students in "team learning" (i.e., the combined "Teams and Teams-and-Mastery" groups) compared with those not in "team learning" (i.e., the combined "Focused Instruction" and "Mastery" groups). The study found, and the WWC confirmed, no statistically significant effects on math achievement for students using "mastery learning" (i.e., the combined "Mastery" and "Teams-and-Mastery" groups) compared with those not using "mastery learning" ( i.e., the combined "Focused Instruction" and "Teams" groups). Finally, the study showed no significant differences among any of the individual groups in the study (for example, "Teams" only vs. "Teams-and-Mastery"). The research described in this report meets WWC evidence standards with reservations. Appended are: (1) Study details; (2) Outcome measure for the mathematics achievement domain; (3) Study findings for the mathematics achievement domain; and (4) Supplemental findings for the mathematics achievement domain. A glossary of terms is included. (Contains 2 endnotes.)