The 2013 study, "Does Working Memory Moderate the Effects of Fraction Intervention? An Aptitude-Treatment Interaction," examined the impacts of the fluency and conceptual versions of "Fraction Face-Off!," a math instruction program designed to improve knowledge of fractions and decimals in fourth-graders at risk for low mathematics achievement. The program emphasizes the measurement approach to teaching fractions and the use of a number line to represent, compare, and order fractions. For this study, students were randomly assigned to three conditions: a fluency group, a conceptual group, and a comparison group. The analytic sample included 243 students. This well-executed study that meets What Works Clearinghouse (WWC) group design standards without reservations found that both fluency and conceptual versions of the program had positive impacts on math achievement. Appended are: (1) Study details; (2) Outcome measures for the mathematics achievement domain; and (3) Study findings for the mathematics achievement domain. A glossary of terms is included. [The following study is the focus of this review: Fuchs, L., Schumacher, R., Sterba, S., Long, J., Namkung, J., Malone, A., Hamlett, C., Jordan, N., Gertsen, R., Siegler, R., & Changas, P. (2013). "Does working memory moderate the effects of fraction intervention? An aptitude-treatment interaction." "Journal of Educational Psychology," 106(2), 1-14.]