National achievement data show that elementary school students in the United States, particularly those from low socioeconomic backgrounds, have weak math skills (National Center for Education Statistics 2009). This study examines whether some early elementary school math curricula are more effective than others at improving math achievement in schools serving a high percentage of disadvantaged students. Understanding the relative effects of math curricula is important because curricula tend to be aligned with particular strategies for teaching math, yet little rigorous evidence exists to support one approach over another.