Thank you all so much for your responses. I appreciate them more than you can know. I admit to tearing up quite a bit as I read through this thread - I guess I am even more emotional about this situation than I realized.
The idea to go and observe is a great one. We did do this already, though, and we were there for several hours. Of course, while we were there, he was on his best behavior. He stayed in circle time, did what was asked, stayed focused on his worked, etc. The teacher joked that we needed to observe every day.
We had an OT go and watch the classroom too. She saw some misbehaviors, mostly that he was not staying in place for long enough. He'd want to jump from work to work.
It's so hard to get a finger on exactly how bad he is acting at school. I don't think the teachers are lying or even exaggerating because I know for a fact that he is a very intense kid and very stubborn too. It doesn't sound like they have found triggers or any pattern to his behavior. He just sometimes decides he doesn't want to cooperate, or he doesn't want to follow the rules.
The last time he got sent home from school was for dumping sand on some girl's head. Part of me thinks that it isn't that strange for a three-year-old to dump sand on another kid's head when they are playing in a sandbox. Is it bad behavior? For sure. Worth kicking him out of school and suggesting medication over? Not really. But, I guess the incident was just part of a bigger picture/pattern of misbehavior.
I can stay home with him this summer. My husband and I both work from home - and I only work part-time. I actually really want to take him out of school right now and keep him home all summer too! My husband, however, really wants to keep him in school. I'm not sure what we'll end up doing.
Much of what many of you said really resonated with me. I do think that he is a difficult kid to have in the classroom, but I don't think they believe the environment is at all part of the problem. They think that if they can't handle him, no one can.
I completely agree with the poster that said for Montessori being a child-led education they sure have a TON of rules. So true. I think I had this idea that they were more flexible than what they really are.
What worries me is that his experiences here are shaping how he sees himself. I feel like he has been labeled (rightly or wrongly) as a troublemaker by both the teachers and the other kids. I also worry about the other kids. If he is as disruptive to the classroom as it sounds like is sometimes is, then that really isn't fair to them.
OK, here I go again... "babbling" out a long post. Clearly, I've needed a place to vent. You all don't know how much I appreciate being able to talk openly about these issues here and receiving such great feedback. It really means a lot. Thank you!