This paper reports on a quasi-experimental pilot study of the impacts of a high school teacher professional development (PD) series. The 10-session series, "Engaging High School Students in Academic Work," was designed to equip teachers to deepen students' learning and engagement and thereby increase course-passing rates. The study took place in a district in the U.S. Southwest that selected two of its interested high schools with similar demographic characteristics to participate, one receiving the PD and the other serving as the comparison school. Longitudinal analyses found statistically and educationally significant impacts of the PD series on four of the five measures in the primary outcome domain (students' course passing) and on teachers' reports of providing extra help. The article discusses limitations of the study and the need for further exploration of how PD can lead teachers to adopt more engaging instructional practices. It offers readers access to all PD materials and invites them into dialogue about how to adapt the PD series and its implementation going forward.