Vance Packard’s 1959 book The Status Seekers describes this school process, noting that while the inherited-wealth elite sent their sons to private boarding schools that were favored feeders for HYP, those colleges maintained their academic reputations with public school students who were actually strong students (the scions of the inherited-wealth elite tended to be satisfied with “gentleman’s C” grades).
Obviously, things have changed since then. HYP are now coed, the private high schools in question now emphasize academics much more, and the strong favoritism for the inherited-wealth elite has been reduced somewhat to donation and legacy preferences in admissions, where the legacy applicants now have to meet high academic standards.