Students will take the standard academic subjects in the morning and do math for 2.5 hours in the afternoon.
Did they discuss how they will have everyone do the same topics at the same time with a population selected for interest but not aptitude?
I think few kids who aren't good at math want to study it for 2.5 hours every day at a math-focused school. Also, the site
http://proofschool.org/faq/ says they are looking for the "truly talented" at math:
You say you’re looking for “math kids.” What do you mean by that term?
By “math kids” we mean children who are truly talented at math. We say we’re looking for students who are internally pulled by math, not externally pushed into it. Of course, math kids have many interests beyond math or computer science–it’s more just a term of convenience and endearment, really–not an absolute. Almost a nickname. If you know any math kids, you know what we mean. Maybe you were one, once, too.