I say, don't take out privileges or do time out. Instead, try to understand why he is driven to aggression and help him. There is ALWAYS a valid reason for a child does. If you can find what it is, you can solve the problem.

So it is not about stopping him, but about listening to him and removing the CAUSE of his aggression.

The book, Raising Our Children, Raising Ourselves, can help you a lot with this. Also, you can take phone advice from the author by signing up on the site www.authenticparent.com