JoJo, that sounds very cool. I would love something like that. (In fact, thinking ahead, I would probably homeschool dd and toss her in afterschool care 5 days a week if I could. I've GOT to have some time to work, but no reason it can't be in the afternoon...) Could you start at grade K? Or "grade ability 1, regardless of age".
Btw, what you said kind of reminded me of what Alexander Dawson's Afterschool Academy: http://www.dawsonschool.org/academics/after-school-academy/index.aspx