Remind me of the details.... have you talked to mom/dad? Is this normal behaviour for him? Are they aware that it's not okay, and must be stopped? If parents are sympathetic to the issues and willing to work together, I will do my best to persevere. How long has this been? When did he start with you?
The fact that he is getting better, even in tiny baby steps, is good news to me. As absolutely frustrating as it is, I would continue with what you have started in the way of consistent behaviour and reactions.