As the possessor of a hot temper myself, I think addressing the symptoms is important, too. (Obviously you want to deal with the cause, as everyone else has already said!)
I found it helpful as a child to be told that anger itself is not intrinsically a bad thing, but like all emotions, it can be productive (where would we be without people who didn't get righteously angry about poverty or injustice, for instance?), or it can be counterproductive (as in kicking your sub!). But you can choose to use your superpowers for good, Spiderman!
Some physical strategies for dealing with the overwhelming nature of anger might also help: my mum sewed pockets on the front of all my dresses, and when I could feel myself getting angry, I stuck my hands in my pockets. As a teen, I found various deep-breathing techniques helpful. These days, if I am getting seriously ticked off about something, I go pull weeds or split some firewood for a while. Anger often needs a physical outlet, but you can't have it be kicking somebody! Maybe you can brainstorm some possible physical outlets with him and his teacher (running on the spot? clapping out the chalk brushes outside?).
He's a smart kid--I think logic will work better than losing recess.
Hope that helps--please ignore if you think it's a bunch of hooey.
peace
minnie
