1. Sitting in the chair does seem to work, but I'm worried that it's somehow stigmatizing. He doesn't seem to mind, but who knows how he's really feeling on the inside. I've tried to ask him, but he just brushes it off. I just don't want him to have an identity of the kid who can't sit still (sort of a self fulfilling prophecy).
I would suggest you have a discussion with your DS about it. Can you explain to him that his moving around is distracting to the other children, and that sitting in the chair is one solution to that? You might tell him that kids learn the skill of being still at different ages, just like kids learn to talk and read at varying ages. If the teacher is open to other solutions, and your DS would prefer a a different (and workable) solution, then great. If not, and he's okay with sitting in the chair, then no harm, no foul. I wouldn't worry too much about stigmatizing him. If the teacher isn't making a big deal out of it, I doubt the other 4 year olds will even give it another thought.
2. Related to the situation above, I understand a teacher allowing a kid to read while walking around, and allowing to certain extent kids to squirm etc. (that's great!). But, what about times like circle time, when it's not academic, but simply a matter of listening to others, being respectful etc. I know he's four, and your right, it should be a learning process--but he could care less and therefore squirms about and is completely distracting to other kids who can sit and listen to others.
My prediction is that you'll see slow/steady improvement over time, and that ultimately he WILL be able to sit still when necessary. You may also want to consider that sitting still may decrease his ability to pay attention. My DS spent so much of his brain power trying to be still in 2nd grade, he frequently had no idea WHAT the teacher had said.
