I checked around a bit and found these articles that might help:

http://www.hoagiesgifted.org/radical_possibility.htm

http://www.davidsongifted.org/db/Articles_id_10180.aspx

http://www.continuinged.ku.edu/is/hs_level.shtml



http://www.smccme.edu/docs.php?section=1&navid=60&docid=540

Does your state offer college courses paid for by the school system? I know some do, and it solves the problem, plus the child gets some free college credits. It looks like a number of states have some sort of program that allows high school students to have dual enrollment in college courses while getting high school credit for them, too. I'd look for that first.

If your state doesn't have such a program, you might be able to make it happen anyway. There's certainly precedent for it. I found such programs in 3 states (my last 3 links) with just a 3 minute google search, stopping at only page 3.

That would be my first choice, since it not only solves your "no more classes" problem neatly, but it also gives your child some free college credits.

If you don't have a university or community college nearby, you could probably arrange online and/or correspondence courses or independent study classes. I designed the correspondence course for composition at the big state university I worked at, and it was as faithful a representation of the in-class experience as I could make it. Not as good as the real thing, obviously, but the students who completed the course and got a passing grade were definitely better at reading and writing than they were when they started the course. They aren't a waste of time if the student takes the course seriously.