So our ABA consultant did their first school observation yesterday and sent me in a wee email just to let me know how it went. And DS is doing really well! Obviously, there are clear areas of need and support, but he 'played catch with three other boys in the playground for ten minutes with 3 other boys, initiating AND reciprocating play throughout'. He generally seems calm, happy and settled.
I know it sounds weird to be so pleased, but its the first independent confirmation I've had that DS is actually happy at school, IYSWIM. It is such a load off my mind. 
Tomorrow the work starts - and there is a big long list - but today is the first day I can picture him in school being happy and safe. I feel like a new woman.