dailydogsbody - does he get angry at school? What methods have you tried? What other threats/rewards does he respond too?
DS1 was always a very emotional child, and at 5 would absolutely erupt with anger, apparently uncontrollably, and just go completely wild. I put it down to his temparament ... that he feels emotions very strongly, and was simply unable to control them.
HOWEVER when he started his new school, (just over 5), they said it was unacceptable and that he should be able to control his temper at that age. They did lots of positive behaviour things - he had a target to not lose his temper at school for a month, and he would get a merit certificate in assembly ... and he did it! I was STUNNED - I didn't think it was possible at all. Over the past year he has continued to improve, and improve ... now he doesn't flare up, he doesn't get so angry so easily, and generally is not 'angry' very often, and when he does he has learned to control it.
Just as an illustration - today has been a bit of a Lego day, he's spent several hours building various models. Just before bedtime - end of the day, worst possible time - I was carrying a model upstairs and I dropped it on the tiled floor, and the whole thing fell to pieces. He was devastated, but completely controlled it, and set to re-building it. 6 months ago he would have screamed and shouted, lashed out at me, screamed and shouted, etc., etc. His reaction today was, I think, beyond his years - so that shows how far he has come.
It is partly age and maturity, but basically what I am trying to say is I WAS treating him as a 2 or 3 year old, and for me it took someone else (school in this case) to say no, this is not appropriate at this age ... and he responded.
This may all not be relevant to your situation, but maybe it is. Anyway hope it's helpful.