I have no idea what the residential college system has to do with it. Schools that don’t have it are just fine. Often the freshman and sophomore years set the tone. If various social clubs on campus that are diverse or for ethnic niches have HUGE influence over social climate on campus, then students are more likely to mix and go to even smaller events hosted by those places. If not, then students (whether they be ethnically uniform or not) will gravitate toward the organization or whatever that has a monopoly. derp claims that this is Greeklife and that it is somewhat ethnically uniform. It may also have to do with how Cosmopolitan students attracted to the school are to begin with. It isn’t about just being smart and having diverse cultures and skin-colors that make people want to mix. It has to likely be something they’ve been very exposed to or always desired before even coming or else the school has do a lot more work to make it happen. At other schools, often it is the international students (particularly those that did not attend international schools) that are hard to "integrate because of this. It just so happens to be fortunate that they are a clear minority (even if a somewhat sizable one 10-20% in most cases). Often domestic students at private schools with say 50-55% whites are fine.