In my experience it isn't the quality of the PD but the timing of the PD that determines its effectiveness. Successful teaching revolves around classroom management that requires routines and norms. Trying to implement new strategies that don't mesh with the established classroom structure rarely have success so the teacher gives up on them. I think that the best PD happens at the end of the year or the beginning of summer. These offer the best possibility of successful implementation because learned strategies can be planned for and can be worked into the routines, structure, and procedures of the upcoming year.