ASD and choosing sixth form

[ThisOneToo]

We are in the process of choosing a sixth form for DS. ASD but masks very well so just comes across as a little bit shy and socially awkward at times. Despite this he has had lots of trouble in making lasting friendships in his current school, has flitted between different groups and also experienced some bullying over the years, all his friends are from outside school. I am not sure what happens at school that makes him so unpopular, outside school he seems popular amongst both girls and boys. He now wants to move schools for sixth form to the same school where some of his friends are. I am not sure that this is a good idea, what if the same things happens there and he loses these friends? He is not unhappy at his current school as such, just wants to join his friends at the other school.

Are his friends outside of school also neurodivergent? I find my kids tend to have the most long term and successful friendships with people who are equally as unique as they are.
If they are then maybe they will be OK at the same school? Plus there is a lot to be said for a fresh start at that age.

I'm not aware of any of his friends being ND though obviously I've not seen their medical histories. They all seem like very ordinary teens, going to parties and hanging out together skateboarding. That's why I can't work out why DS is so unpopular in school when he has so many friends otherwise, whether it's something he does in school that he doesn't do outside school?