"Saxon Math" is a curriculum for students in grades K-12. The amount of new math content students receive each day is limited and students practice concepts every day. New concepts are developed, reviewed, and practiced cumulatively rather than in discrete chapters or units. This review focuses on studies of "Saxon Math"'s primary courses, which include kindergarten through pre-algebra. The What Works Clearinghouse (WWC) identified five studies of "Saxon Math" that both fall within the scope of the Primary Mathematics topic area and meet WWC group design standards. All five studies meet WWC group design standards with reservations. Together, these studies included 8,855 students in grades 1-3 and 6-8 in 149 schools across at least 18 states. "Saxon Math" had mixed effects on mathematics test scores of students in primary courses. Four appendices are included: (1) Research details for Agodini et al. (2013); (2) Outcome measures for the mathematics achievement domain; (3) Findings included in the rating for the mathematics achievement domain; and (4) Description of supplemental findings for the mathematics achievement domain. Contains WWC Rating Criteria and a glossary of terms. [For the 2016 Saxon Math Intervention Report, see ED565884.]