Chics, I'm sorry about the school issue, that is truly a pain. I know that here the teacher staffing ratios are different for kids in diapers/pullups vs. potty-trained kids. The preschools we looked at actually had an iron-clad policy of a certain number of accidents per month disqualifying the kid, so of course we had one that refused to train until over age 3. On the bright side, he was perfect after that, but I know that doesn't help your child care situation. I tend to agree with Math Ace-- your son might be better off in a school with less of a reputation but where he's not seen as a kid with the problem.
Good luck to you.
Good luck to you.