Four core principles should guide the professional development of teachers:
1. Make sure that the teacher evaluation system has the capacity to drive professional development.
2. Eliminate professional development that groups teachers together because they happen to be in the same school or district.
3. Look as much as possible to the expertise, talent, and skills of teachers working with teachers as the most sustainable form of professional development.
4. Use external consultants for new undertakings where internal expertise may be lacking, but have a plan for growing that expertise.