My son did exactly what you are describing. He was a "peer model" in a preschool program through our school district. It was an incredible experience for him. He did it for two years.
Pros:
I wanted him in an academic environment, not a basement of a church somewhere. I wanted certified teachers (his had national certification) and I wanted him to get a feel for what his school would be like.
He went to PE, art, music, had reading buddies with third graders and was completely prepared for kindergarten. The bonus was that he had a poor pencil grip and the OT for the atypical kids helped him out.
He learned compassion. He doesn't stare at kids with disabilities because he interacted with them daily. Was not intimidated by braces, wheel chairs, etc. He learned patience with the kiddos that had learning disabilites. He would be paired with one and help them finish the project.
Cons:
He picked up on some poor behaviors. We fixed that at home with conversations about why they acted the way they did and how it wasn't okay for him to do that. He had to set the example for them.
Sometime, obviously, the atypical kids required additional attention, so my son had to take care of himself on occasion. This was few and far between, but it's something you need to be aware of.
Bottom line, ask questions. Lots of questions. How many para/teacher's aides are in the classroom to assist? How are behavioral issues handled?
It will be so helpful for some of these kids to have a positive peer model. Think about it, ask questions, and good luck!