Go to the web sites of venture capital, private equity or hedge funds, or of Goldman Sachs, and you’ll find that HYPS alums, plus a few Ivies, plus MIT and Caltech, are grossly overrepresented. (Equivalently, look at the founding teams of venture funded startups.)
Most top firms only recruit at a few schools. A kid from a non-elite UG school has very little chance of finding a job at one of these places unless they first go to grad school at, e.g., HBS, HLS, or get a PhD from a top place. (By top place I don’t mean “gee US News says Ohio State’s Aero E program is top 5!” — I mean, e.g., a math PhD from Berkeley or a PhD in computer science from MIT — the traditional top dogs in academia.)
This is just how the world works. I won’t go into detail, but it’s actually somewhat rational for elite firms to operate this way — a Harvard guy knows how the filtering works at his alma mater and at similar places so he trusts it. Plus, at the far tail of ability I would guess the top 10-20 UG schools grab almost 50 percent of the pool.
I teach at U Oregon and out of curiosity I once surveyed the students at our Honors College, which has SAT-HSGPA characteristics similar to Cornell or Berkeley. Very few of the kids knew what a venture capitalist or derivatives trader was. Very few had the kinds of life and career aspirations that are *typical* of HYPS or techer kids. At the time I took the survey almost 50 percent of the graduating class at Harvard was heading into finance. You can bet that the average senior at Harvard knows what Goldman Sachs is (and even what it means to make partner there), that McKinsey is so over (relative to careers in finance), what the difference is between a Rhodes, Marshall and Churchill scholarship, etc. etc. Very few state school kids do … Last year a physics student at Oregon won a Marshall to go to Cambridge. The administrators were happy about the PR. I had a conversation with a vice-provost about how to ensure a steady pipeline of such candidates — but there are not the resources, institutional understanding of the process, etc. (let alone pool of able kids) to turn UO into a Rhodes/Marshall/… machine like Harvard.
Now tell me that peer or network effects don’t matter. Controlling for SAT may account for much of the variance in well-established careers like medicine or even law, but for the very top jobs (which contribute disproportionately toward income inequality), kids at elite schools have huge advantages. Guess where I will send my kids (assuming they can get in)?
To see the elite / non-elite divide most starkly, look at the probability of (earned) net worth, say, $5-10M by age 40. This cuts out almost all doctors and lawyers and leaves finance, startups and entertainment (i.e., movies or television; let’s ignore sports). Even after controlling for SAT, I would guess elite grads are 3 or maybe even 10 times more likely to achieve this milestone.
Controlling for IQ doesn't account for differences in drive or life expectations or naked ambition, let alone social networks, signaling or information flow among elites.
See also Returns to elite education.