D.T.
Why can't they discipline at school?! That's horrible. The behavior is unacceptable and he needs to learn. Discipline is simply teaching right from wrong - surely the school can do that! I can see not punishing, but not disciplining? I"d switch schools.
If he was older you could do a chart like thing where if he acts up at school you withhold a privilege at home. However, 2.5 years old is much too young for that. By the time he'd get home he would've forgotten what he did and it would be very hard to make that connection.
I'd talk with the teachers and start looking at other schools. It may be something relatively little like cussing now, but if they won't discipline for that there's a good chance they won't discipline for bigger/worse behaviors as the kids get older.