80% of kids at elite schools come through the same kind of feeder system of either good local public schools or private schools. In that system there's a serie

80% of kids at elite schools come through the same kind of feeder system of either good local public schools or private schools. In that system there's a series of successively narrower hoops you have to jump through - if there's only one junior high that teaches math beyond a certain point and not everyone can go there, those kids are going to be better prepared for the high school that teaches more advanced things, so they'll make up a disproportionate amount. Since it's really hard to on the track once you're not on it, at every level of evaluation and selection you keep selecting out of smaller and smaller sections of the initial pool. The people who come out of that system tend to be supremely competent, but in a limited way. If you take a stand in high school approaching a topic from a different angle and a teacher doesn't like it and gives you a C (the horror), when it comes time to apply for Harvard there are an essentially limitless number of competitors who didn't and who got the A. So people who naturally play it safe and cynical tend to move on, and people who don't tend to adapt or get cut.