I think there is often a benefit in the application process for being "geographically diverse". Is this what you mean? So if I had applied from my rural Texas school, I would have gotten a boost for being diverse on that count. But that is because it is so much less common for such students to apply. But I would have lost out in any legacy points or letters of recommendation from alum or esteemed educators. Plus my school did offer less in terms of extracurriculars and more advanced curriculums (no AP classes offered at all). So I think, despite my IQ, my application would not have looked as good as someone with a lower IQ and more access to these social and cultural extras.
For the most part though, I would guess that private prep schools and magnet schools across the US are the usual pipeline to elite universities. I went to the University of Chicago for grad school and I know they recruited alot of their undergrads from particular private schools across the country.
