I agree that all the schools in the local area will be known by a college. So I don’t think a star student will be meaningfully advantaged or disadvantaged in Stanford admissions by attending Paly or Gunn vs any of 15 other high schools in the mid-Peninsula (more Paly and Gunn students may attend but those two are also more competitive high schools).
My point is that an unhooked ORM student applying to (say) Princeton or Yale or Brown may have a better outcome if they attend Paly or Gunn compared to the other nearby high schools that are less well known on the east coast, because there aren’t many spots for that type of kid.
I’d expect Ivies like the ones you listed to have a regional admission officer that is familiar with the Bay Area, beyond just Paly and Gunn, but one can certainly swap out the Bay Area for an unknown high school that has little history. For example, suppose a student applied from a small high school in a low income area of Wyoming. It’s possible that the lack of knowledge about the HS could put the student at a disadvantage, and it’s also possible that the colleges might favor the applicant because he/she is from a unique background compared to the applicant pool.
I expect it depends on the specific applicant, HS, and college. Things like how much/little information the GC provides about the HS could have an influence. While all this could have an influence, I’d be less confident about making sweeping conclusions such as attending Palo Alto High or Gunn is a better choice for Bay Area kids, if you want to attend an Ivy. I don’t think we can draw that conclusion.
I almost posted some of that stuff about Princeton, but to show children of Princeton employees have a huge leg up in admissions there. Princeton is in a more rural/isolated location so it’s easy to see the local advantage. A lot harder for schools like Harvard that could have so many other factors.
My original point about HS in college towns wasn’t about getting into the local school. I was saying a student at the best HS in Ann Arbor, Charlottesville, Boulder, Athens, etc. have a unique advantage and leg up in admissions because they have easy access to research, theater programs, writing seminars, etc. Also, it’s not the only way for an “average excellent” to get a bump in admissions, but it’s easier to live in or near to one of these towns versus get a faculty job at Princeton.
The original question was “How does the high school you attend impact admissions?”, and I think there are also high schools where the competition is so great that it can be near impossible to be a top student. The Bay Area seems to be a place where this happens. So many smart hard working students!