"Saxon Math", published by Houghton Mifflin Harcourt, is a core curriculum for students in grades K-12. This report includes studies that investigate the potential impact of "Saxon Math" for students in grades 6-8. A distinguishing feature of the curriculum is its use of an incremental approach for instruction and assessment. This approach limits the amount of new math content delivered to students each day and allows time for daily practice. New concepts are introduced gradually and integrated with previously introduced content so that concepts are developed, reviewed, and practiced over time rather than being taught during discrete periods of time, such as in chapters or units. The What Works Clearinghouse (WWC) identified five studies of "Saxon Math" that both fall within the scope of the Middle School Math topic area and meet WWC evidence standards. One study meets standards without reservations, and four studies meet standards with reservations, and together, they included 6,601 students in grades 6-8 from 52 schools in four states. The WWC considers the extent of evidence for "Saxon Math" on the math performance of middle school students to be medium to large for the mathematics achievement domain, the only domain examined for studies reviewed under the Middle School Math topic area. Appended are: (1) Research details for Resendez & Azin, 2006; (2) Research details for Crawford & Raia, 1986; (3) Research details for Peters, 1992; (4) Research details for Resendez, Fahmy, & Manley, 2005, Cohort A; (5) Research details for Resendez, Fahmy, & Manley, 2005, Cohort F; (6) Outcome measures for the mathematics achievement domain; (7) Findings included in the rating for the mathematics achievement domain; and (8) Description of supplemental findings for the mathematics achievement domain. A glossary of terms is included. (Contains 7 tables, 21 endnotes and 1 additional source.)