Thanks for all the input. I still don't know if I'm going to do it, but you guys have definitely given me some points to consider. Colinsmum - attendance is important here, too. But since we're halfway through the year and so far he has perfect attendance, I don't think one day will be too awful. Besides, this will certainly not be a regular thing. Maybe 2-3 times during a school year AT THE MOST.
Grinity - basically, the school's gifted program is a joke (30 minutes a week, and it's in the same classroom with the rest of the kids). He's not learning a thing in school because the curriculum is dumbed down to the lowest common denominator. His teacher tries, but she has 14 other kids in the class and her hands are tied by idiotic district policies. She's open to letting him read higher level books, tries to have enrichment projects for him to do whenever possible (again, she has 14 other kids - so she simply CAN'T keep him challenged as much as he should be), and even let me send him some worksheets to do when he is done with his class assignments. But he still has to do regular assignments, which bore him to tears and he sees them as a waste of his time (which, to be honest, they are). I spoke to administrators about possibly skipping a grade. They're resistant to doing it at all, but won't even consider it until the end of the year (which I suppose is understandable). When a seven year old starts telling you without being prompted that he needs something harder to do at school, you know there's a big problem.
I am a little worried about skewing his attitude about school, though. It's sad, but I'm thinking if we can just fight through elementary school, he will have more options when he hits middle school and it may be easier. But not if he learns to hate school by that point, and he's well on his way already. In any case, if I do let him do this, I want him to see it as a learning opportunity and not as a reason to just take a day off. And I certainly don't want him to start thinking that regular school attendance is not important.