Hey,
I'm so pleased your son is doing better, my son is actually in exactly the same position. Definitely ADHD, perhaps autism, but also struggles with hyperactiveness and sensory issues. The school have been fantastic with him, even though he is not diagnosed yet. Here are some things that helped us:
Regular communication with the school, we have 2 week meetings to discuss behavior, what's going well, what isn't.
That you are doing the same coping mechanisms at school and home. Even down to the words you say, my son's biggest phrase is: we use our words, not our hands. I make sure I use this and so does the school
When something happens at school, like an incident, and they HAVE dealt with it, then it doesn't need bringing up again with the child, unless the child brings it up and you can talk about it calmly.
Our child has a quiet room at school, when he's cross or angry, he can take himself into the quiet room and there are sensory toys in there, ear defenders, busy boards. He has made amazing progress from this alone as he also struggles with self regulation.
Making routine very clear. He has a sticker chart for when he completes all his morning routines. Come in, put coat and bag away, listen to the teacher, start work. He gets a sticker
When there is going to be a change of routine, allow plenty of notice. Ie when my little guy is playing, the teacher will say, right Fin, we are going to finish in 5 minutes, then we are going to do some reading. They have even invested in a digital alarm, so he can see the countdown and hear when it's transition time.
Our child (may not be the same as yours) really doesn't do well on an empty tummy and doesn't know when he is getting peckish. So he is allowed extra snack breaks. They find that when he has had a snack he is SO much more cooperative.
Hopefully some of these will help or you can try as coping mechanisms. Don't be afraid to ask for meetings from the school and lay down what you expect and what you dont want. I had to tell them in the end, that unless it was critical I knew about an incident (ie a child got injured by my child) then I didn't need to know. I found it really helped with my anxiety. Also allows you to think what happened in school can stay in school (unless it is important that you know or can help like I said before)
But above all, you are not alone, he will NOT be the only child who has ADHD or difficulties and it is their duty to meet his needs. I am battling it too, but just know you are doing an amazing job x