"Students would learn more outside the classroom if exposed to young people from a greater variety of backgrounds than they’d typically find at a top-tier college."
I had a roommate from Westchester NY and one from inner city Baltimore.  I grew up on a farm in Colorado.  The only thing we had in common was that we all got into the same top-tier college.
The author is erroneously equating academic capability with diversity. 

BTW - I guarantee that if you had a dorm with 1/2 elite college students and 1/2 vocational students they would separate themselves with maybe two in a hundred that would actually "cohort" with the other group.  People separate themselves and group according to similarities, always have.