The Common Core State Standards (CCSS) have been developed in response to the criticism that students in the U.S. are graduating from high school without being college and career ready and that they are falling behind their counterparts in other countries in key subject areas. In this work, the authors report the results of an efficacy study that investigated the impact of Math in Focus: Singapore Math ("MIF")--developed by Houghton Mifflin Harcourt (HMH) that, according to the program developer, provides comprehensive support for CCSS. The research questions are as follows: (1) Is there a positive impact of MIF on student skills in mathematics problem solving?; (2) Is there a positive impact of "MIF" on student math procedural skills?; and (3) Is "MIF" differentially effective in its impact on student achievement depending on (1) the ethnicity of the student? (2) the incoming achievement level of the student? The research took place during the 2011-2012 school year across twelve elementary schools in one urban school district in Nevada. Ninety-three teachers of grades 3, 4 and 5 were recruited to participate in the study, with 41 teachers randomized to the "MIF" group and 52 teachers randomized to the control group. Rosters were provided for 2235 students in participating teachers' classrooms. The design was a group randomized trial lasting one year. A two-level hierarchical linear regression model to estimate the impacts of "MIF" on student achievement. The study gives preliminary evidence concerning the impact of one CCSS-aligned math intervention on student performance on two mathematics strands. Tables are appended.