Being stuck in a lower level class is torture, and as long as a kid is getting social interaction its gonna be okay. did you try asking him? 6 year olds understand a lot, and at the very least he gets an option to say no. if you ask it's not dictation, its cooperation. And as he gets older, KEEP asking. and could those high school level classes count as high school credits?

I am a stringent believer in the idea that school is not for socialization. and if your child is old enough to go to school with seventh graders, he can probably make friend with them if he wants too.

Where does he want to be?