Students often struggle getting along with their roommates, which sometimes leads to a desire to return back home.  To increase the likelihood of roommates getting along and ultimately retaining, try pairing them with students who have similar interests, live similar schedules, and enjoy similar living arrangements. 

Many campuses already do this via expensive 3rd party software programs.  But, it can also be done cheaply with a simple paper roommate matching profile form. If you are not doing this, give it a try.