The good public schools have more funding thanks to pTax, more extra-curriculum programs, but more importantly …. the fellow students are presumably more serious, more disciplined, even if they don’t yet show “self-direction”. Family upbringing is the neighborhood is the key factor in my view.

The higher academic standard is, in my view, a by-product of the school culture (校风). I am not sure if the innate talent of students are higher in a good public school vs a regular school. But if students work harder (mostly due to parents’ effort) for many years, they will be able to learn faster, absorb more and tackle higher academic challenges. The stronger foundation and study habits make them more capable learners, even if they weren’t more intelligent in the beginning. I blogged about this in https://1330152open.wordpress.com/2016/08/16/roller-coaster-academic-competition/