I think I'd deal with the issue of grade if and when you decide to put him into a conventional school. At that point you can tell them whatever you want. Maybe you'd want to give an above-grade level test the spring before he goes to the new school, but that and a list of what your child has been studying is about as much as you'd need, I think.
Unless it's a case like that of Erica's DS, where he wants to compete with intellectual peers in some forum, it seems mostly unnecessary to worry about grade. You know?
I have been known to answer "what grade?" questions when they won't accept age as an answer with "He's working on decimals, so whatever grade that is" sorts of answers. Only with close friends, though. I mostly figure there's no real reason for random people to know too much about our business!
