It might be all the disruption with the schooling your son is reacting too. It is not easy being the new kid all the time, I know I hated changing schools. It is especially hard if you are a sensitive reserved person. Fitting in, making friends can be hard.

However he needs to learn that being rude to you is not acceptable. Each time he is rude, do time out in a boring room in the house such as the laundry or spare room. No books, toys, tv or anything during this time. Leave him for 8mins and then he is to say sorry for the behaviour. Be consistent, calm, no smacking but don't tolerate it. One warning then time out but explain why the behaviour is unacceptable.

With respect to his education, have you considered home schooling? I know it is not for everyone but it might give him more continuity and there are networks for socialisation and you can also do other social stuff like sport, Karate etc Also have you looked at alternative schools like Steiner or Montessori, their approaches may suit your son better as they aren't as rigid as conventional schools and it is child led learning. Anyway just a thought. Hope things get better.