It would be simple to assume that in this period of rising college costs and economic difficulty, the most cost-sensitive students would come from the lowest-income families. But a large portion of those families have been priced out of the market for quite some time, and those that haven't and are strong students continue to have access to strong scholarship and aid packages. (I am not suggesting that lack of access is a good or overlook-able matter--just that the situation is not tremendously different now than they were five years ago for those families.)
So if faculty and administrators at private colleges are looking for a group that is a bellwether of cost-sensitivity, I would recommend not low-income families but a different group--families we call "no-need merit." Prospective students who fall into this category earn some sort of academic scholarship, but because of their family income, they receive no other aid--not Pell Grants, work-study, or institutional grants.
These families are particularly cost-sensitive for two reasons. First, without any additional aid they face the prospect of paying ten to twenty thousand dollars a year for college. Second, no-need merit families are more likely to have a college-going culture, so if the cost at a private college seems too high, they are likely to choose a lower-cost public alternative. Watching the performance of no-need merit prospects, then, is a key way to see the impact of college cost on the size and composition of the entering class.