Challenging/unusual behavior always tells us something. What do you think he is trying to tell you/his teacher by not doing his work all of a sudden? Could it be that he wants to sit alone and therefore he stops working so that he gets put in time out?

Is there anything that preceeds his not doing work or antecedents that the teacher has noticed?

You're already looking at environmental factors, which is great. What about physical or medical factors?

What does he mean when he says that others 'disturb' him? Is there anything in common the kids who disturb him have that could give you an idea as to what it is about them that is disturbing him? Or is it random in that any other kid could disturb him?

Sorry 101 questions lol. Just trying to thought provoke..

Does he tell you why he's not making friends in this class? Did he make friends in prep/kindy? Are there any of his prep/kindy friends in his class? You say he's social so there has to be another reason why he's struggling to gel with his classmates. Maybe because he's so bright, he's just having trouble connecting with them on his level.

I agree that it's a possibility that he could be dumbing himself down.. hence the no work. Do other children notice his abilities? He doesn't need to skip a grade does he?