Don't get me started on bus discipline!My DS has got into trouble twice.
In Y8 he got into fisticuffs with a Y7 student who was calling him 'gay'!
As he was in the year above he was deemed to be more responsible. They both got sent home by taxi (which went on the school bill
) The bus hadn't left the school car park at the time the incident happened.
Last year (Y9) someone threw a sandwich at him which was wrapped in foil - he threw it back and it hit a girl on the head.Unfortunately this girl's brother was the bus monitor and reported DS but not the person who threw the sandwich at him! He got a Saturday detention for that little carry on!
I don't think there is much you can do really in this situation except tell DS to try and ignore it. Personally I think if you intervene it will make matters worse for your son. If he doesn't rise to the bait they will get fed up and move on.