Purpose: The purpose of this study was to explore how the Advanced Placement Summer Institute (APSI) supported Advanced Placement (AP) teacher's instructional needs considering the expansion of the AP program in recent decades. Design/methodology/approach: A survey including Likert-style and open-ended questions was distributed to participants at one East Coast APSI to gather data, which were analyzed quantitatively. An exploratory factor analysis (EFA) was conducted on the Likert items to identify latent constructs, and two logistic regression (LR) models were run to predict what features of the professional development (PD) improved teacher perception of APSI. Open-ended constructs were analyzed by identifying and describing common themes. Findings: The findings indicated that APSI improved teachers' perceived content knowledge and pedagogy and improved teachers' perceptions of their ability to better support student achievement, but that more focused professional learning was needed in working with academically diverse student learners in AP courses. Research limitations/implications: This study was limited to analysis of perception of teachers who attended one APSI training site, making it difficult to generalize without repeated measures. Originality/value: This is the only multidisciplinary study connecting literature on effective PD to an analysis of the effectiveness of APSI for AP teachers.