We had a Halloween themed contest last year in October, I thought it was a bit disappointing in that nobody tried to make a scary movie despite the theme "Fright." I guess it doesn't motivate me to want another similar contest soon.
October is likely to be a *very* busy month for me because I have to film a large live action project then, so if I'm running this contest I'd really like to have it in September. I have an idea for a themed, month-long contest in September; as far as school schedules they really are different from place to place; in the case of the United States the back to school date varies from district to district, there's not much uniformity.