School's Div vacancies for Special Assistant cannot be found in open posting. Your colleague has been recommended by your P and endorsed by Supt for the posting. I was an SA a few years ago. There were 5 of us in the tea session and all of us got in. I supposed ZDs usually trust the endorsement of the P and Supt.

As long as you have a stint from HQ, I would say that it would help you in one's career because the 2 to 3 years spent in HQ will widen your perspectives. Some div like SD are more hard to get in due to the fact that the vacancies are not even found in APEX.