"Math Expressions" is a curriculum for students in prekindergarten through sixth grade that aims to build students' conceptual understanding of mathematics and to develop fluency in mathematical problem solving and computation. The curriculum encourages student learning of mathematics through real-world situations, visual supports such as drawings and manipulatives, multiple approaches to solving problems, and opportunities for students to explain their mathematical thinking. This What Works Clearinghouse (WWC) intervention report, part of the WWC's Primary Mathematics topic area, explores the effects of "Math Expressions" on general mathematics achievement. The WWC identified three studies of "Math Expressions." One of these studies meets WWC standards. The evidence presented in this report is from one study of the effects of Math Expressions on students--including 37% White, 33% Black, 27% Hispanic or Latino, 2% Asian, and 1% American Indian or Alaska Native students--in first and second grades in urban, suburban, and rural districts. [For the Intervention Brief, see ED612618. For the Intervention Snapshot, see ED612619.]