BTW: this kind of thing is definitely not limited to a situation like this, i.e., acceleration. Any time a kid is different in any way, kids will say hurtful things. The best thing you can do is to just be there to talk it through with him.
I've also seen this happen over many different situations, when one child stands out in one way or another. Sometimes it even happens where really there isn't anything all that noticably different, but a group of children just for whatever non-reason chooses to exclude or make fun of another child. I agree with the advice you've already received, but would add one thing. In my children's experience, school culture can make a *huge* difference when this happens. I was just talking with my kids on the way home from school today about a situation in my dd's class where one student was being mean to another, and even she noticed how differently it was handled at her current school than it would have been at her previous school. The key is that the school she's at now has a staff that acts swiftly when they see instances of children excluding others or bullying or whatever. Treating each other with respect is an ingrained part of the school culture and the teachers expect to address problems like this immediately and directly with the students. I don't know what the attitude or policy is at your charter school, but I would let your ds' teacher know that this has happened and how it's made him feel -his teacher(s) may have some good ideas about how to address the issue in school.
Best wishes,
polarbear
