[Chris Patton]

I know this is old-fashioned, and I may be completely vilified for suggesting it, but has anyone considered punishment?
You've mentioned that the parents have a good behaviour chart to reward him when he behaves well, but what about when he doesn't?
I'm not talking about physical abuse, I think in this sort of case sing corporal punishment would probably make things worse, but what about denying him things he enjoys when he misbehaves?
Maybe its so simple that it hasn't been mentioned, or maybe it just isn't being considered. Is he being sent to bed without being allowed to play/watch tv? Is he being denied his dessert or other treats when he misbehaves?
Positive reinforcement of good behaviour is great, but punishment for bad behaviour is also very effective.