S.W.
Before considering a therapist, I would look at how much physical activity he gets each day. All kids need lots of exercise and most do not get enough. This can result in aggressive behavior.
Any type of activity is good, especially if he enjoys it. My daughter and I are both training in Karate. This has been a great experience for both of us. It redirects aggression and teaches self-control and confidence. I highly recommend any type of martial arts for all kids - aggressive or timid. We go to National Karate, and there are other good ones in the Mpls area.