A top school is a good signal for how much time someone spent studying in high school, except for affirmative action students who get into top schools with much worse scores and GPA.
While this is true it highlights a major misgiving in the attitude with regards to the reality of socioeconomic status. If your poor, yes you theoretically have the ability to utilize those resources, but what good are those resources if you don't have a conducive environment to engage in study?
Lower socioeconomic status is correlated with lower stages of Maslow's Hierarchy of Needs. Self-actualization i.e reaching one's potential is more dependent on the satisfaction of basic and psychological needs, which are generally more accessible to those of privilege.
It's not just about resources being available, it's resources being available and making sure people have the opportunity to engage in those resources.
This dismissive "quota tokens" attitude really irks me. It's one thing getting in, it's a total different ballgame surviving and coming out the other end with a decent GPA. I've seen people of all socioeconomic backgrounds fail and some from remarkable poor backgrounds do exceptionally well.
For the truly competitive schools, the affirmative action students still need very high scores and GPA, they just tend to be given a little more of a pass on the extracurricular activities and essays in the application. I'd argue that for the most part, students of any demographic have to do some pretty crazy things to get the attention of top schools. The probabilities of an affirmative action student being granted admittance are just much higher than for an equivalent non-affirmative action student, but that doesn't mean that affirmative action students can get away with having poorer grades and scores. I'd argue they just have to be less well-rounded.
Assuming all high schools are the same.
There are virtually an infinite number of variables that contribute to university admission and it's extremely reductive to suggest that it's purely a function of the amount of time a student spent studying in high school.