It could very well be that your son's body is overloaded (or is insufficient) in key elements it needs to work. If the body is missing nutrients, it WILL show up as behavorial problems.
Take your son to a naturopathic doctor and have him tested for heavy metals (it is a very simple, 24-hr urine test). My daughter has Sensory Processing Disorder (SPD) and used to have an unbelievable temper/anger issue, too. When she was 7 years old, I became very sick and started doctoring with alternative doctors. One of the tests they ran on me was a heavy metals test; I found out I had SEVERE heavy metal toxicity. After I did some research on the Internet and saw all of the effects/side effects of heavy metals in the human body--many of which my daughter exhibited--I began to wonder if her SPD wasn't caused--or at least a by-product--of heavy metals (we also discovered that both she and I have a genetic liver mutation that doesn't allow our bodies to detox correctly, making heavy metals accumulate in our bodies. That test was run by the Mayo Clinic.). I had her tested too.
You know what? Her report for SEVERE heavy metal toxicity was EVEN HIGHER than mine! And I was 40 years older than her!
She chelated 3-4 times, and the anger issues diminished so much, it was like having a new child in the house. We also switched over to all organic food, have reverse-osmosis water, eat farm-raised/pasture-fed meat, stay away from fast food and processed/prepackaged food as much as we humanly can, and we've been transitioning away from household/outdoor chemicals/pesticides/etc. to organic ingredients. We also discovered we have food allergies and intolerances and stay away from those foods as well.
Food--nutrition--really DOES impact everything about us, including our psychological welfare. My daughter also took some amino acids that helped "fill in" what her brain was missing; that also helped.
My daughter is now 11 years old, and I am so thankful I went through all that work when she was 7 years old. I can not imagine still having to deal with the fights and the screaming and the running away and hiding and the defiancy. I can't believe that I put up with it all for 7 years! Don't get me wrong; we're heading into the tween and teen years, and there will be some of that. But we can manage everything now, and my daughter has learned coping mechanisms to help her deal with and get through difficult situations.
It is likely that, for your son, it is a biological issue that needs to be addressed by a doctor (like a naturopath) who is trained in nutrition, toxins, and how the body responds to them and who has the training to help get the body detoxed and then rebuilt back up again (in lost or missing vitamins, minerals, amino acids, enzymes, etc.).
Helping your son now will pay off in big dividends later. He will learn better in school if he's able to concentrate, and you'll have better family relations and a better peace of mind.
Good luck!