Billions of dollars are spent annually on professional development (PD) for educators, yet few randomized controlled trials (RCT) have demonstrated the ultimate impact PD has on student learning. Further, while policymakers and others speak to the role schools should play in developing students’ civic awareness, RCTs of PD designed to foster civic learning are rare. This randomized controlled trial contributes to the knowledge base on the effectiveness of PD designed to integrate civic learning, ethical reflection, and historical thinking skills into high school humanities courses. The study examined the impact of a PD intervention in two areas: (a) teacher self-efficacy, burnout, and professional engagement and satisfaction; and (b) the academic, civic, social, and ethical competencies of 9th and 10th grade students in the teachers’ classes.