This article reviews research on the achievement outcomes of mathematics programs for middle and high schools. Study inclusion requirements included use of a randomized or matched control group, a study duration of at least twelve weeks, and equality at pretest. There were 102 qualifying studies, 28 of which used random assignment to treatments. Effect sizes were very small (weighted mean ES=+0.03 in 40 studies) for mathematics curricula, and for computer-assisted instruction (ES=+0.10 in 38 studies). They were larger (weighted mean ES=+0.18 in 22 studies) for instructional process programs, especially cooperative learning (weighted mean ES=+0.42 in 9 studies). Consistent with an earlier review of elementary programs, this article concludes that programs that affect daily teaching practices and student interactions have larger impacts on achievement measures than those emphasizing textbooks or technology alone. Appended are: (1) Studies Not Included in the Review; and (2) Table of Abbreviations. (Contains 4 tables.)