The study authors examined the impact of "Responsive Classroom," a professional development program for teachers, on student achievement. This study took place in a large, ethnically and socioeconomically diverse district in a mid-Atlantic state. The intervention was implemented during 3 school years from 2008 to 2011. Study authors randomly assigned 12 elementary schools to implement "Responsive Classroom" for 3 years and another 12 elementary schools to a comparison group that would not implement "Responsive Classroom" during that period. Intervention group teachers began receiving training for "Responsive Classroom" in summer 2008. However, the researchers discovered that some teachers in two of the comparison schools also received training for "Responsive Classroom." As a result, the authors randomly selected one of these two schools and re-assigned it to the intervention group, so that the intervention group ultimately consisted of 13 schools and the comparison group consisted of 11 schools. Study authors assessed the effectiveness of "Responsive Classroom" by comparing student performance in math and reading on a state standardized test in fifth grade. These students were in third grade during the 2008-09 school year, the first year that "Responsive Classroom" was implemented in the intervention group. There were about 1,000 students in the intervention group and 1,000 students in the comparison group. None of the analyses presented in this study meet WWC standards, and therefore, the study findings are not presented in this WWC report. A glossary of terms is provided. [The following study is the focus of this "Single Study Review:"Rimm-Kaufman, S. E., Larsen, R. A. A., Baroody, A. E., Curby, T. W., Ko, M., Thomas, J. B., Merritt, E. G., Abry, T., & DeCoster, J. (2014). "Efficacy of the Responsive Classroom approach: Results from a 3-year, longitudinal randomized controlled trial." "American Educational Research Journal," 1-37. doi: 10.3102/0002831214523821.]