Policy changes at the federal and state level are endeavoring to improve student achievement at schools serving children from lower-SES homes. One important strategy is the focus on using evidence-based core reading curricula to provide a consistent framework for instruction across schools. However, rarely have these curricula undergone rigorous comparative testing. Therefore, the purpose of this study was to compare the effects of six core reading curricula on oral reading fluency growth, while appraising whether these effects differ by grade level and for children living in lower socioeconomic (SES) households. Over 30,000 students in first through third grade Florida Reading First classrooms comprise this academically and economically diverse cross-sectional. Hierarchical Linear Modeling was used to model latent growth curves for students' reading fluency scores over the school year. Growth curves revealed differences across curricula as well as between students of lower and higher SES, suggesting that reading fluency growth trajectories for curricula varied depending on student SES and grade level. Findings indicate that while there are similarities among curricula, they sometimes differ in their ability to promote reading skill growth. Differences by grade level and SES were also detected. However, many of these differences were small. Implications for the use of curriculum as a conduit for improving reading instruction are discussed. (Contains 3 figures and 6 tables.)