Anon78100- I am not sure of the answer to your question. I do know that teacher professional development involves obtaining additional training in order to better serve the school and eventually offer more opportunities to the teacher who is now considered more marketable.
Often professional development programs for teachers can include seeking an additional endorsement or area of specialization. For example, an elementary teacher might seek an ESOL endorsement by taking additional courses in teaching English as a second language.
Also, a teacher might seek a Masters degree in special education which is considered a critical shortage area in most school districts.
This allows the teacher to earn significantly more because of the Masters degree and would offer an even higher starting salary as well as given a bonus because of the degree in the critical shortage area.
In addition, many school districts offer teachers looking to specialize in critical shortage areas tuition assistance. Usually this is in the form of loan forgiveness, in which a teacher does not have to pay back their student loans.