Principals shape the academic setting of schools. Yet, there is limited evidence on whether principal professional development improves schooling outcomes. In 2008-09, Pennsylvania’s Inspired Leadership (PIL) induction program required that newly hired principals complete targeted in-service professional development tied to newly established state leadership standards within five years of employment. Using panel data on all Pennsylvania students, teachers, and principals, we employ difference-in-differences and event study strategies to estimate the impact of PIL induction on teacher and student outcomes. We find that PIL induction improved teacher effectiveness (in math) and student math achievement, and that the effects of PIL induction on teacher effectiveness were concentrated among the most economically and academically disadvantaged schools in Pennsylvania. Principal professional development had the greatest impact on teacher effectiveness when principals completed PIL induction during their first two years in the principalship. We also find evidence that teacher turnover declined in the years following the completion of PIL induction. We discuss the implications of our findings for principal induction efforts.