Just seen this thread, and your ds sounds so much like one of mine!
I really think the school are letting you down tbh. If my ds had been excluded from primary every time he hit someone he would have missed so much school!
My son is very lively, obsessive, driven, impulsive and unfortunately quite agressive at times. Last year, he really clashed with the teacher, and she couldn't cope with him. Ever week, I was getting called in for something, often twice a week. She was an excellent teacher for my eldest, very strict, and I thought she'd be good for him, but she just couldn't reach him. At home, he is fine, we know how to get responses from him, and he does not misbehave int he same way. He also does better with adults rather than other children.
We also had the whole hair thing. It makes me a bit cross that it is something that is picked up on with boys. If he wants it long, that's his choice! Mine finally agreed to a hair cut a few weeks ago, actually. He is now 7.
Anyway, my oldest son is on the spectrum somewhere, and I don't personally feel these issues are typical of asd. But I recently had to do the connors 3 test for adhd for my eldest as part of his whole diagnostic process, and that REALLY set alarm bells ringing. I am now thinking of requesting it for my youngest. I ran him through it after doing ds1 and he scored very highly in some areas. Your son sounds so similar to mine, I think it might be worth you looking into it.