@itssquidstella
You might find that there are quite a few children like him at the super selective grammar, if that's where he ends up.
That is the kind of place where mine transferred for sixth form, after five years of supportive education, intensive on site OT and SLT, a low arousal environment and forming a group of peers. No bells, clear routine. Music and PE adapted to individual needs.
He left with ten GCSEs. They all got a clutch each. Plus a computing qualification each. He still meets up with his two best friends from there and a couple of others more occasionally.
Once in selective sixth form, he immediately bonded with a gang of aspie chaps and they are now all second jobbers after good degrees and excellent unis, and still meet monthly for a pint and chat. A tight core group who also socialise with the other ex grammar students. It was a lovely social sixth form and a good fit.
I know there are several ways to skin this kind of cat, but I will describe our path, in case it’s a useful template for anyone.
Every now and then I bump into someone else who did similar and exchange war stories, so I know it’s increasingly been an option over the past decade and people do win expensive packages through ECHPs by insisting on making a parental application for the ECHP even against school and council reluctance. CAMHS often provides the testing and reports that saves the day by proving need, or otherwise private Ed psychs, OTs, SLTs.