Hi again engmom,
I went back and reread your first post and realized that you are switching from private to public. So the public school really doesn't know your child yet.
The thing about public school (I think?), is that they move very, very slowly. My guess is that they have to fill out a ton of paperwork and send it off to the state to justify that a kid needs to be accelerated. They will not let a kid jump a grade without a mountain of paperwork to justify it. Just thought you should be warned in advance. It might also be state specific and even district specific, depending on how friendly your school is to acceleration. But I would start working on generating that mountain of paperwork. Try to get as much concrete data on your child as possible, or start hounding the school to start testing him.
Good luck!
