Sounds like my oldest Aiden. For us, unfrotunately the desire to blend in "broke" him and we had to remove him from school to eventually homeschool. This was after 2 and a bit years in a formalised pre school environment.
The only way we found around this was to mix him with loads of different age and different ability kids all the time - to actively encourage him to ignore age and grade levels on all products and games.
I also did a lot of talking and showing about things that are all different (like leaves and bananas and fingerprints etc). It's a lot better now after nearly 2 years out of that environment - he still will try blend in at cubs (but thats okay cause he is the youngest for now) and at church (again okay cause it's a couple of hours once a week and I can cope with the fallout)
It's hard but definitely something you need to try help him with.
best of luck!
