This study used a mixed-methods explanatory design and Mezirow's transformative learning theory to explore the experiences of new school principals in a professional development leadership program and its influence on their self-efficacy as leaders in a Midwestern urban K-12 school district. Surveys, semi-structured interviews, reflection notes, and analytical memos were used as data sources. Key findings included (a) transformation in perceived self-efficacy resulting from program participation and (b) engagement in critical reflection on their role as school leaders. The findings suggested that new principals need support following the leadership training and more research on their experiences after assuming leadership roles.