Any advice re ASD (in dx process) 12 yo (aggressive) son, please?

[43er]

Please, please - does anyone have any advice? My son is 12 and has just started secondary school. He is very physically mature and strong. He has responded very aggressively to the change and has hurt other children. The school are supportive, but obviously very concerned about their duty of care responsibility (rightly).
His behaviour is escalating on an almost daily basis and he has just starting squaring up to me when we are alone (if angry). He doesn’t do it if other adults are present. I am no shrinking violet, but, given his recent violence towards others, I am starting to feel afraid. Currently, I try to respond briefly and calmly, and then walk away.
He’s bright and articulate - he came out of primary school with a very good set of SATs - but everything is being eclipsed by this huge aggressive force within him. We live in a reasonably clise-knit community and I know that other children and parents perceice him to be out of control and dangerous. We are increasingly isolated.
DS has really struggled to conform to behavioural expectations since he was 3 and has many ASD characteristics, hence the move to diagnose.

[43er]

close-knit perceive