Huh? Don't most public schools offer various levels of the same subject for this reason? Like remedial, honors, AP, etc. In what way is this problem solved by private schools? Unless you're implying that home schooling solves this problem, which yeah sure if one of the parents works full time teaching their children and also has a high level of education themself as well as the relevant skills. Not something that can actually be scaled out across the country. And history has shown that homeschooling typically leads to inferior education.

The schools that spend the least per student have the best scores

Yeah that doesn't sound right at all. You got a source?

[–] Robust_Mirror@aussie.zone 12 points 2 weeks ago

Here's some sources:

A $1,000 increase in per-pupil spending over 3 consecutive years led to a full grade-level improvement in both math and reading achievement

A 10% increase in school spending improved test scores by 0.05 to 0.09 standard deviations

Out of 18 statistical estimates examining the relationship between spending and test scores, 11 showed positive and statistically significant improvements

Oh wait these sources agree with you and that guys probably full of crap.