This study explored if the Advanced Placement (AP) World History: Modern Reading is effective teacher professional development (PD). The researcher used a mixed methods explanatory sequential design. A survey was completed by 83 AP World History: Modern high school teachers who had attended the AP World History: Modern on-site Reading. The researcher then conducted a focus group discussion with eight participants to study teacher perceptions of the Reading experience. Quantitative and qualitative results were integrated in order to gain a deeper understanding. The researcher found that attending the AP World History: Modern on-site Reading is beneficial teacher professional development. The structure of the in-person Reading allows for collaboration, engages participants and is relevant to the attendees' classroom practice.