Hello Mary Ann! Maybe this can come in useful: http://www.teacherpolicyresearch.org/TeacherRetention/tabid/99/Default.html

Overall, school leadership and teacher retention are two different variables that need to be operationalized first. If you cannot get the actual data on retention, you can measure turnover intentions. There are simple meausres for that, e.g. Article Predicting teacher retention using stress and support variables

Good luck!