There is a critical need to improve the pedagogical content knowledge of in-service physics teachers because of the large population of under-qualified teachers in the physics classroom. The need is even greater for the advanced placement (AP) physics teacher because of the level of rigor involved in the AP curriculum. This case study examined how participating in additional physics focused professional development influenced the instructional practice of AP physics teachers in a southeastern state of the United States. Fourteen AP teachers who received College Board training were purposefully selected from high schools in the state. From this population, seven teachers who experienced additional physics-focused professional development beyond the College Board training (APD) were compared with the other seven teachers with little or no additional in-service physics focused training (NAPD). The analysis of the quantitative data from the classroom observation indicated that there was a large treatment effect difference between the APD teachers and the NAPD teachers. The qualitative data from teacher interviews, surveys, and questionnaires was thematically analyzed and the result indicated that the APD teachers increased their PCK level after the intervention. In addition, the study found that although contextual factors influenced the type of instruction used by the teachers, these factors were more teacher-based than context-based. Due to the small sample population, the findings from this study represents initial empirical evidence of the influence of the intervention on the instructional practice of the AP physics teachers.