How to Attract Students
1. Student "sleepovers" provide information to the prospective student that is both valuable and likely to influence the final decision, but ...
2. There is a lot of noise in the signal.
The information is valuable because it gives the prospective student a feel for the student society in which she will be immersed for four years if she goes there. It is noisy because student society varies a good deal even within a single college, and what part she gets exposed to depends on who her "sponsor"--the student whose dorm and room she is doing the sleepover in--happens to be.
I conclude that a college could increase the number of students who choose to go to it by investing more resources in matching sponsor and prospective student. Some schools clearly make some attempt to do this, as judged by conversations I had at two of them. On the other hand, at least one of the schools my daughter visited did a spectacularly bad job, and one a spectacularly good job, with the result that the latter is currently her first choice.
Of course, there may be schools with ideological reasons not to engage in such matching. If a prep school prospie is unimpressed by a host from the inner city, or a football fan prospie by a shakespeare quoting host, that may just show, in the view of some schools, that the prospie is too narrow a type for them to want, however good his or her SAT scores, grades, etc. There may even be schools which see the sleepover as an opportunity to educate the prospie by exposing him or her to a different sort of person.
The former, at least, is not a wholly unreasonable position, although on the whole I would be inclined to see it as a negative, not a positive, signal about the school. On the other hand, the school where my daughter most strongly felt that her host and her friends were her sorts of people--the sorts who spent their free time talking and singing, not watching television--was also the one where she most felt that her own multiple oddities were seen by the students she met as interesting, as assets not liabilities.
Which is to say that, in her perception, that particular student society was the one that appreciated diversity--in the sense relevant to an academic environment, not the usual sense of a euphemsm for affirmative action.