The availability and subsequent expansion in the use of online learning environments has provided a new avenue for teacher professional development: blended learning. While blended learning environments may provide attractive benefits to teachers and school administration, the impact of blended teacher professional development has been largely unexamined in the existing research. This mixed-methods study investigated professional development outcomes for 64 teachers participating in district sponsored teaching professional development, 32 in a blended course and 32 in a face-to-face equivalent of the course. Outcomes of the professional development were measured using pre- and post- instructional belief surveys, participant satisfaction surveys, and interviews measuring retention of instructional beliefs and application of new instructional strategies. Additionally, participants who did not complete the course were interviewed to learn about their experience in the course and reasons for non-completion. The results of this study show similar changes in instructional beliefs for both the blended and face-to-face sections and significantly higher satisfaction with course content, materials, and instructor involvement among blended participants. However, blended participants were less likely to be transitioning to, or practicing new strategies as measured by interviews 12 weeks following course completion. A large number of blended participants showed evidence of their knowledge of new instructional strategies, but were reluctant to apply new strategies in their classrooms. Non-completers primarily cited lack of time for their withdrawal, but expressed an interest in future blended learning courses. The recommendations from this study should inform districts, schools, and teachers about blended learning for teacher professional development.