As Lionheadlover says rexes are wonderful, but can suffer more commonly from ailments that other buns do not.
I also agree that bunnies are not generally the best pets for children. I have 13 rabbits, and two kids aged 12 and 5. We've had bunnies for about 4 years. In every instance the rabbit is my pet, I would not have my children responsible for them and generally my lot do not like to be picked up (the rabbits that is!) they are happy to have the kids sit with them and be stroked and fed but I would not allow my children too pick them up etc.
From that point of view as a classroom pet I dont think bunnies would be particualrly suited, whatever the breed. And as others have said if they are to be moved from home to school regularly this could upset or stress them and stress can cause problems with a bunnies delicate digestion system.
Would you not consider another animal?