Principals shape the academic setting of schools. Yet, there is limited evidence on whether principal professional development improves schooling outcomes. Beginning in 2008-2009, 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 5 years of employment. Using panel data on all Pennsylvania students, teachers, and principals, we leverage variation in the timing of PIL induction across principal-school cells and 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 increased student math achievement through improvements in teacher effectiveness, and that the effects of PIL induction on teacher effectiveness were concentrated among the most economically disadvantaged and urban schools in Pennsylvania. Principal professional development had the greatest impact on teacher effectiveness when principals completed PIL induction during their first 2 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.