I wouldn't punish a kid at home for something that happened at school - it just makes a bad day worse. Reward a good day by all means but how would you feel if you had a hellish day at work and your partner made home horrible because of it rather than being supportive and helping you sort things out before the next day?

Like someone said the one line email may be a screening device. Obviously they don't want kids changing classes willy-nilly but if you persist you may find it is not impossible.