If his condition is severe enough for him to be diagnosed already you need to be looking at specialist schools. And you need to be doing it now because you’re likely to have a massive battle lasting several years to get him the support he needs
That’s not correct in severity correlating to age of diagnosis. My child, and many were diagnosed young, prior to school or in first year of school (after being on the waiting list for some time prior when issues had been identified), and none of them would have really qualified for specialist units. A few parents actually pushed for it until visiting a few and finding they only really catered to what would have been known in times gone by as ‘low functioning’ autism and not kids who can be very academically able. It seems to be a real gap unfortunately, which is a shame for everyone and should be addressed but I doubt it ever will be.
My child sat under their desk for the first three years of schooling and refused to participate in class. They did do some work under the desk though, but not much. This sort of thing marks the child as ‘weird’ to other children, which is why they do not get invited to parties. Long story short, eventually my child came out from under the desk, eventually they participated in more class work, eventually they actually even did tests, eventually they met others like themselves and became genuine friends, eventually they got to do specialist subjects they were actually interested in which allowed them to flourish and show their true abilities, get into a competitive uni degree and then get a great job in a specialised area.
I really wish there was a different/seperate schooling system that accommodates children like mine so they would have had a positive schooling experience in the primary/lower high school generalist years but there is not. My friend though was incredibly grateful for a spot in a specialist school for her child with autism, as they needed somewhere safe to send them of a day so they could work. Their child, in their 20’s, is now in institutionalised living, non verbal, not toilet trained, and permanently heavily medicated for their own and others safety, which apart from the sedating medication aspect is pretty much the same state as when they started school unfortunately😞.