LOL! I hear you!
The main reason we're HSing this year is because DS6's behavior was awful in 1st grade, and he had always been the most rule-oriented kid you'd ever want to meet for the entire rest of his life before that. But once 1st grade started, he was angry, frustrated and nasty to be around. Being bored stiff for 7+ straight hours will do that to a kid! It's disrespectful to him, really. Treat someone like they're dumber than they are, and they get annoyed, you know? Even/especially kids!
The very day we took DS6 out of school, his behavior improved. He has his bad days, of course, but overall, he's back to his sunny happy self, and went back to it surprisingly fast. The longer the child is bored, the longer it takes to get back to good behavior, from what I understand.
Never underestimate the power of childcare for preserving your sanity!