It's interesting that school improvement and development research on effective strategies for professional development highlights the importance of collaborative and collegial learning environments; environments that help develop communities of practice able to promote school change beyond individual classrooms. This suggests that leadership, culture and a professional learning approach are critical issues that need to be addressed before other interventions will work.
The research also strongly suggests that short 'quick fix' inputs have limited impact and that sustainable, long-term change requires high-quality, coherent and intensive support... most colleagues I know knew this anyway! In a review of nine studies, Yoon, Duncan, Lee, Scarloss, and Shapley (2007) found that sustained and intensive professional development was related to student achievement. The studies of professional development lasting l4 or fewer hours showed no effects on student learning, whereas other studies of programs offering more than 14 hours of sustained teacher learning opportunities showed significant positive effects. The largest effects were found for programs offering between 30 and 100 hours spread out over 6–12 months.
This suggests that the most effective approach to teacher development and support would be to use intensive introductory sessions supported by regular and sharply focused refresher sessions over a long period where teachers can discuss their developing practice and work together to discuss emerging issues and solve problems.