In the elite higher education economy, low-income students are an investment many colleges aren’t willlling to put money on. And it’s showing in enrollment.

Federal data show that low-income student enrollment at selective colleges hasn’t grown from the 1990s through 2012. In some places it hovers beneath 15 percent, while the higher education sector overall saw large increases in low-income students attending college, The New York Times reports.

Richard Pérez-Peña reports:

Colleges generally spend 4 percent to 5 percent of their endowments per year on financial aid, prompting some administrators to cite this rough math: Sustaining one poor student who needs $45,000 a year in aid requires $1 million in endowment devoted to that purpose; 100 of them require $100 million. Only the wealthiest schools can do that, and build new laboratories, renovate dining halls, provide small classes and bid for top professors.

As Pérez-Peña points out, legal attacks on race-conscious admissions policies mean universities have been turning to other means, namely a socioeconomic-based approach, to boost diversity. It’s not clear that a class-based approach, while more palatable to some, will be all the more alluring to universities. “Higher education has become a powerful force for reinforcing advantage and passing it on through generations,” Georgetown University professor Anthony Carnevale told The New York Times. “College presidents are under constant pressure to meet budgets, improve graduation rates and move up in the rankings. The easiest way to do it is to climb upstream economically – get students whose parents can pay more.”