- The rolodex factor.

- The fact that people that go to Harvard are already smart, and they would be successful anyway.

http://www.nber.org/papers/w7322.pdf

I'm not sure if this is a generally available link; I am using it from a Stanford IP which may have purchased access. The paper is Dale and Krueger, "Estimating the Payoff to Attending a More Selective College: An Application of Selection on Observables and Unobservables."

But 4 years out of college, I can say that the salaries of my friends with no college degree and significant marketable skills are much, much higher than the salaries of my Amherst friends with English, history, or foreign language degrees. Like 4x higher. What you study seems to make a far bigger difference than where you go to school.

Here's what I'm getting at: As per the article, parents who send their kids to an elite university to get a degree in creative writing aren't doing it because they're under the impression that they're getting vocational training, and nevertheless, it's probably a smart investment. Class cohesion is a pretty powerful force.

(Note: With all of this I'm not saying this is a good thing; just that social factors are as powerful as skills in determining at where someone falls in the economic ladder.)

The problem is (particularly under the current US system) is that it is very hard to distinguish between likelihood to succeed & likelihood of going to a good college @ 18.

There are also feedback effects like mingling with those likely to succeed.