"Saxon Math" is a textbook series covering grades K-12 based on incremental development and continual review of mathematical concepts to give students time to learn and practice concepts throughout the year. The series is aligned with standards of the National Council of Teachers of Mathematics (NCTM) and various states, and can be adapted for special education students in inclusion classrooms, pullout programs, or self-contained resource classrooms. Although content differs by course, the incremental, distributed approach of "Saxon Math" is the same, with mathematical concepts presented in a series of short "lessons" intended to gradually build understanding and previously-taught concepts practiced and assessed throughout the course. Developed in the early 1980s, "Saxon Math" included four middle school math textbooks used in the studies included in this intervention report. The series has been redesigned and now offers three textbooks for middle school grades. This report includes studies that investigate the potential impact of Saxon Math texts on math achievement of middle school students but does not include these revised texts. One study of "Saxon Math" meets What Works Clearinghouse (WWC) evidence standards, and four studies meet WWC evidence standards with reservations. The five studies included over 6,500 students from grades 6 to 8 in 52 schools in four states. Based on these five studies, the WWC considers the extent of evidence for "Saxon Math" to be medium to large for math achievement. The WWC reviewed 19 studies on Saxon Math. One study meets WWC evidence standards; four studies meet WWC evidence standards with reservations; the remaining 14 studies do not meet either WWC evidence standards or eligibility screens. Based on the five studies, the WWC found mixed effects on math achievement. The conclusions presented in this report may change as new research emerges. Appended are: (1) Study characteristics: Resendez & Azin, 2006 (randomized controlled trial); (2) Study characteristics: Peters, 1992 (randomized controlled trial); (3) Study characteristics: Crawford & Raia, 1986 (quasi-experimental design); (4) Study characteristics: Resendez, Fahmy, & Manley, 2005, Cohort A (quasi-experimental design); (5) Study characteristics: Resendez, Fahmy, & Manley, 2005, Cohort F (quasi-experimental design); (5) Outcome measures for the math achievement domain; (6) Summary of study findings included in the rating for the math achievement domain; (7) Summary of subscale findings for the math achievement domain; (8) "Saxon Math" rating for the math achievement domain; and (9) Extent of evidence by domain. (Contains 14 notes.) [The following study meeting WWC evidence standards, is reviewed in this intervention report: Resendez, M., & Azin, M. (2006). Saxon Math randomized control trial: Final report. Jackson, WY: PRES Associates, Inc.]