Actually, it appears TCU undergrad enrollment in on a par with that of other BCS private schools. Undergrad enrollment at Notre Dame, 8,371; Duke, 6,500; Vanderbilt, 6,879; Northwestern, 8,400; Wake Forest, 4,400; Boston College, 9,000.
Where Duke, Northwestern and Vanderbilt outdistance TCU is in grad school enrollment, which obviously points to their more elite academic status. Had a school of that reputation been what the conference was searching for, Tulane would have been the choice.