The What Works Clearinghouse (WWC) reviewed interventions to promote middle school students' math knowledge and skills. Because there is some variation in how school districts organize middle school, we considered curricula aimed at students in grades 6 through 9, covering one or more of the following content areas: numbers and operations, algebra, geometry, measurement, and data analysis and probability. Only core, comprehensive math curricula were eligible for inclusion in this review. These curricula extend over the course of one semester or more, are central to students' regular school instruction, and are based on any combination of text materials, manipulatives, computer software, videotapes, and other materials. The WWC looked at 361 studies. Of these, 203 appeared to be studies of practices or other interventions that did not qualify for our review. Of the 158 remaining studies, 21 studies of 7 curricula met our evidence standards, 4 without reservations and 17 with reservations. Altogether, the WWC looked at 34 interventions: 7 had studies that met WWC standards with or without reservations and 27 had studies that did not meet WWC evidence screens. No eligible studies were identified for an additional 16 programs at the time of this review. (The identification of eligible programs ended in September 2005, and that of eligible studies in July 2006.) The WWC rated the effectiveness of middle school math curricula based on the available research evidence. In looking at math achievement for the 7 curricula: "I Can Learn[R] Pre-Algebra and Algebra" had positive effects; "Saxon Middle School Math" had positive effects; "Cognitive Tutor" had potentially positive effects; "The Expert Mathematician" had potentially positive effects; and "UCSMP Algebra" had potentially positive effects. Two other curricula had mixed effects on math achievement. (Contains 2 tables and 1 figure.) [The following studies met WWC standards and are reviewed in this intervention report: (1) Morgan, P., and Ritter, S. (2002). An experimental study of the effects of Cognitive Tutor Algebra I on student knowledge and attitude. Retrieved November 22, 2006, from http://www.carnegielearning.com/research/research_reports/morgan_ritter_2002.pdf; (2) Kirby, P. C. (2006, October). I CAN Learn[R] in Orleans Parish Public Schools: Effects on LEAP 8th grade math achievement, 2003-2004. (Available from the ed-cet, Inc., 2301 Killdeer Street, New Orleans, LA 70122); (3) Baker, J. J. (1997). Effects of a generative instructional design strategy on learning mathematics and on attitudes towards achievement. "Dissertation Abstracts International," 58 (7), 2573A. (UMI No. 9800955); (4) Williams, D. D. (1986). The incremental method of teaching algebra I. Kansas City: University of Missouri; and (5) Baker, J. J. (1997). Effects of a generative instructional design strategy on learning mathematics and on attitudes towards achievement. "Dissertation Abstracts International," 58 (7), 2573A. (UMI No. 9800955).]