The obvious low hanging fruit is that most Americans just need less school and should skip straight into vocational training which can start as early as 15-16. These kids don't need to ever be even close to calculus or physics. There's an epidemic of overly educated people and it's a tremendous waste of resources and broken expectations.
Just follow the people who invented kindergarten :))
I think kids have a right to be exposed to these ideas. Stratifying society even further, only exposing select sections of the population to advanced ideas in philosophy or science, will not help build a solid democratic society.