I hear what you're saying, but I'd be less angry furiously peeved about how he's being treated than worried that he will fit in badly due to his younger behavior in the fall. I'm already worried that my son's goofiness will be an issue in the fall-- this can with a certain breed of teacher result in opposition to your son, you, or further acceleration.
I'm not saying he has to be older than he is, or that the teacher shouldn't take into account his biological age, but he will ideally adapt too and try to fit in; it's a constant process. Failure to follow classroom rules and routines is an often cited reason for denials of kindergarten or early grade skips. Maybe your son should try not to get dragged into random bits of goofiness in class for a while. Do you think he'd be able to handle that?
Also, I understand your reasons for feeling the way you do, but I don't feel that the teacher was really out of line. Your son should try to act more mature, especially if he's heading into the third grade. Third grade, even more than second, is about fitting into a routine that includes classroom rules and often homework, and increased writing. These are areas that seem to often challenge gifties after a grade skip, and I think it's best to work on any weak areas if at all possible.
This is the struggle we're faced with when we keep our kids in the public school, which can unfortunately be exacerbated by teachers with poor understanding.
(ETA: st. pauli girl makes good points about playing up/down-- my hope too is that he gets to be with grade mates at camp next year. Maybe that's all it is.)
