Hi Dumbledoresgirl, I don't have any direct experience of this but I've just called a friend of mine who does. She has a very bright son who had similar problems integrating at school after they moved countries five years ago - he was 10 at the time. He was deeply, deeply miserable and became very introverted for a long time and his parents sought treatment from a good child psychologist (it took them a good while + a shed-load of determination to find one he 'clicked' with but they got there eventually). The psychologist first advised them to take him to a GP for a thorough assessment to rule out any physical cause. Once they'd done that the treatment basically involved three things (1) encouraging him to open up and express his feelings, (2)trying to change/re-align his thought processes (3) developing positive strategies to overcome problems (4) helping my friend/his mother to deal with her own anxiety.
I've summarised the treatment below:
Expressing feelings: involved kicking a ball around a yard while talking, being encouraged to express his feelings through drawing and writing (this could be done on the computer too - whatever medium appeals most to the individual child works best), sending the therapist e-mails, keeping a journal, having a private "thought box" in his parent's bedroom in which he could post when he was distressed or at any other time
Changing/re-aligning negative thought processes: involved keeping a list of his fears, encouraging him to confront them slowly, step-by-step, then writing down in a column alongside whether the fears were justified or as bad as he had perceived them in retrospect
Developing positive strategies to overcome specific practical problems (such as making friends) involved him and the therapist coming up with some potential strategies and then visualising them, discussing potential fears and role-playing different scenarios.
Reading your thread, you come across as a really devoted and sensitive mother. Hope it works out for you.