Aggression. 4yo starting mainstream school

I haven't posted about my son before. Brief recap. He turned 4 in August and started mainstream school 3 days ago. No official diagnosis yet, end review is 11th October.

I had been to school and had meetings with the head and given her his profile of what he's like and also a copy of all assessment reports. Nursery gave them some bits but tbh nursery weren't particularly helpful.

So before he started the head teacher had me sign forms to start towards EHCP. This school start kids full time but I had explained he should be phased in doing mornings until October half term then add in lunches as I don't think that will go well.. Work up to full time eventually. Turned out there was a 1:1 who's experienced with ASD kids ready for him on his first day! Thankful for this, she is with him each morning except Wednesday so someone else was with him today.

He doesn't have sensory issues with noise, it's mostly people and groups that are his problem. He behaviour was much worse when starting which I had expected. He can get rather aggressive, hitting and head butting which I was most worried about. He has been doing this each day. Today he has hurt other children but also he had gone for the 1:1 and head butted her so much so she actually cried!

We aren't as yet getting any kind of support and I'm at a loss of what to do, I've told school he's much worse since starting in and out of school but what can I do? He must be overwhelmed. I agree others shouldn't have to accept violence but as his mum it upsets me that he can't help this and doesn't know how to react. I don't know how to help him.