@disappointed101 breathe and have a large glass of wine
It will be okay. And the state secondary may very well turn out to be the best and most supportive option for him. Even private schools that claim to be nurturing with small classes aren't always great at dealing with SEN.
I totally second @mimbleandlittlemy, I have a 15yo with diagnosed ASD/ADHD who in Y6 was so immature and so vulnerable, and we too wanted a small independent school for secondary (same reasons as you, small class sizes, nurturing etc etc). He did obtain a place but it wasn't right for him and we ended up taking him out and putting him back into the state sector - back to the school where lots of children from his primary school went.
I won't say it has all been absolute plain sailing because it hasn't but the state option has worked far better for DS because
- he felt comfortable being back amongst his friends/other peers he knew at the state school
- he was actually much happier in a class of 30 - small class sizes freaked him right out (felt like a bunny in the headlights)
- the private school was very sporty with 3 double sports periods a week and he hated it, he was much happier in the state system with one bog standard PE lesson a week!
- he does far, far better self-esteem wise in an environment with a natural spread of ability - the private school spooked him because it was academically selective and he felt as if everyone was much cleverer than him - in his state school he is top or second set for everything and feels much happier
- the "small school, small class size" thing can offer a disadvantage that we hadn't thought of at first. To be blunt, 90% of any year group will see DS1 as weird, the remaining 10% might be similarly quirky/immature/socially vulnerable and therefore be a potential friendship pool. In a small school that friendship pool is by definition very very small indeed. In a larger one, far more potentially quirky children and a much larger potential friendship pool.
DS sits GCSEs this summer, got great mock grades (we are just hoping he does as well in the real thing!), has a lovely group of similarly quirky friends and has a place at his chosen sixth form to study A levels. But most importantly he is happy! I have not regretted, not for one moment, taking him out of the private school. Don't get me wrong there have been stressful moments and difficult moments but school are very supportive. I do genuinely believe that on the whole the state sector is better at looking after DC with SEN.