The purpose of this study was to analyze the impact of a professional development (PD) program on teacher self-efficacy and classroom practice. Thirty-eight in-service teachers from a foundation school in Izmir participated in this study. Multiple sets of data for this study came from the Turkish teachers' sense of efficacy scale, classroom observations, focus group interviews and a PD evaluation form. Collection of data was completed in two consecutive semesters, fall 2006 and spring 2007. Multivariate analysis of variance results indicated that the PD program had a positive effect on all three self-efficacy beliefs. PD courses on instructional grouping (whole-group and small-group instruction) and project-based learning (seminar plus workshop) were more frequently reported as having provided the most benefits to teachers' PD. In conclusion, an instructional practice change did occur in some individual classrooms, but this was not part of systemic school-wide change. (Contains 2 tables.)