This paper presents evidence from an innovative teacher professional development (TPD) project tackling school-related gender-based violence (SRGBV) in primary and lower-secondary schools in Cambodia. The core activities of the TPD project are discussed, focusing on teachers' changes in attitudes and beliefs toward emotional abuse and physical violence against boys and girls, as well as gender equity. The TPD was evaluated using a pre- and postintervention study, and a treatment and control group in Battambang and Svay Rieng provinces, respectively. A total of 151 teachers responded to the questionnaire at baseline (October 2018) and there were 149 teachers in the postintervention period (October 2020). To improve the comparability between the treatment and control groups, we estimated a difference-in-differences analysis in combination with propensity score matching. Only two treated teachers were not matched to the control group, with the final sample consisting of 298 observations. Findings indicate moderate to small effects on changing attitudes and beliefs about SRGBV in both primary and lower-secondary schools. Furthermore, teachers from primary schools benefit the most from the TPD; that is, they engage in less SRGBV. In secondary schools, the effects on engaging in emotional or physical abuse are not significant.