You're not wrong... but doing that right, over an entire population is really hard. I think there is some attempt to do this in many schools. Kids skip grades, kids stay back. There's honors programs and remedial programs.

Honestly, I think the main reason we aren't doing better educating our kids is because no one wants to pay for it. Education is expensive. Rigorous testing of methodologies and re-educating teachers is expensive. We pay our teachers a pittance... I don't know how anyone expects education to be great when we aren't trying to attract brilliant people with high salaries.