This cluster randomized controlled trial investigated the impact of project-based learning with professional development supports on social studies and literacy achievement and motivation of second-grade students from low-socioeconomic status school districts. At random in within-school pairs, 48 teachers were assigned to the experimental or comparison group. Experimental group teachers were asked to teach four project-based learning units designed to address nearly all social studies and some literacy standards. Comparison group teachers were asked to teach social studies as they normally would except to teach a target number of lessons. The experimental group showed higher growth in social studies and informational reading but not writing or motivation. Greater consistency with project-based learning session plans was associated with higher growth in writing, motivation, and reading.