What does the school say? Have they suggested having a talk to the Guidance Officer? I would recommend having a chat to her or him. They are psychologists who work within the school and they may be able to give you a better idea about things that you can try.

Some kids are just angry kids and need management strategies for it, they need to not be pushed too hard when they are feeling like that and they need to have a way to vent their emotions. Some of the kids I have worked with responded really well to having some time out to build with lego, or bouncing a ball against a wall or even just having a stress ball in their pocket that they can squeeze until they are feeling calm. Kids like that tend to not respond really well to someone being in their face and trying to calm them down. Sometimes they need space. Have you tried using cool down - a comfortable place where he can go when he starts to feel it is getting too much for him.

I can't guarantee that they will work and you won't find anything that works first time every time, but it is good to have a range of strategies in your tool kit.

Good luck It's not easy.