I didn't say there weren't other factors, there clearly are, but there are real differences in smarts between schools and to consider this controversial is something I think is more of a product of our present moment than something that people really deep down believe.
And I actually think I can speak to this with some amount of personal experience. I've been at both a lower tier college and a best-in-the-country university. When I was 11 I wanted to learn how to write software so I took courses nights, weekends and summers at the near by college until I was 14. I know how smart the class was and it was no where near as smart as the engineering students at the top tier university.
But that is ok! I think we overvalue intelligence in modern society, but to pretend that there are no differences is undervaluing the truth for the sake of political correctness or ideology.