I had a similar thing with my son when he was 8. At playtime the other kids kept away from him (it was a new school for him and he wasn't making friends). I raised my concerns with the headteacher and she watched him in the playground and casually spoke to a couple of the kids to find out what was wrong. It turned out he was a bit loud and lively and kept tryign to play the fool - this was his way of trying to make friends, but it put the othe kids off and they became irritated by him. We had a chat and he said he was just trying to make the kids like him. He was also tallest in class and it was a bit too much for the others all round. I told him to calm down and just be pleasant to the others, to listen to what they had to say and not to force himself on them to much. If he has no one to play with, I told him not to push in on other's games. This worked perfectly. The kids came to him and asked him to play and he did so, and a year and a half on he is very happy and has lots of friends. This may not be the same situation as your son, but it may be worth approaching the school to see if they can watch what is happening and give you an idea of what the problem is?