I spoke this AM with a friend who has the big local SAT/ACT test prep and college app counseling business.
He told me that the "new" thing in college admissions is figuring out ahead of time who is "likely" to enroll, if accepted. They know that with the common app, kids will apply to many schools at $50-100 a pop, of which most are back-ups. DS's best buddy (Nat'l Merit scholar finalist, 36 on ACT) was rejected by U Mich. My friend said, they didn't believe he would actually enroll.
The main goals of any admissions department are: 1. Have low acceptance rate in order to prove exclusivity of the school, 2. Have the highest yield acceptance divided by enrollment) in order to show how effective the admissions department is. Rejecting a candidate who will not enroll kills two birds with one stone.
I'm sure there is an algorithm for predicting who really will enroll...or someone trying to sell one.
My buddy suggested to those on a wait list, or even those who have been rejected, if school x
REALLY is choice number 1, to call/write the school and flat out tell them that and that you will enroll if accepted. If you are being honest in that claim, you have absolutely nothing to lose.
If you haven't called, then do so.
Best of luck!