Alas, even Richard Dawkins is not interested in starting a school for atheists.
Call me cynical, but is it because atheists don't think they themselves believe in anything worth communicating to others? No, the flood of books on the market by these evangelical atheists ("the good news is, life is meaningless") would disprove that theory.
Surely the atheists are morally upright and concerned about the future, and hence about education. Why no charter school with a STEM focus? Or a private school founded by a rich atheist (surely God doesn't just bless the theists!)?
Perhaps the reason is that they are happy with the public schools. Seriously.
Why start a school that incessantly talks about the God Who Isn't (as an atheist school presumably would) when you can send your child to a school that simply ignores that same Non-God? Ideally, an atheist might prefer an Atheist Academy, but Agnostic Public School works just as well and it's a lot more convenient.