Some schools schedule professional growth during in-service orientation, the week or so before school begins in the fall. This seems to work well, since everyone is fresh, eager, and relatively unpressured. Some sessions are required, others optional. Some have found an off-campus retreat to be helpful in focusing on the issues at hand. Although it is true that most teachers need their summers to recover from a demanding school year and prepare for the upcoming year, summer is an ideal time to hone one's teaching skills.
Some schools require summer reading, college courses, or projects.
Undoubtedly the most popular window of opportunity for staff development is during those days set aside during the school year devoted exclusively to teacher training, when there are no students on campus. While the students have the day off, teachers are free to attend a teachers' conference or seminar. Perhaps teachers would be free to observe at other schools. Release days, when selected teachers are given the day off school, are another alternative. Polls show that such set-aside days are understandably popular with teachers.