Usually, when a demographic group is significantly underrepresented on elite college campuses, we consider it a problem. But there is one such problem that almost no one seems to notice or care much about. Nearly 30 percent of college undergraduates are adults, defined by the United States Department of Education as 25 years old or older. But at Stanford, the share of undergraduates who are adults is 1.2 percent; at Yale, 0.7 percent; at Princeton, 0.6 percent; at the University of Chicago, 0.2 percent.

This blatant discrepancy hasn’t drawn any sustained attention even from liberal elites who otherwise tend to notice these things. That’s a testament to the notion many of us carry around in our heads, often based on our own experience, that colleges are places filled with fresh-faced young people who recently graduated from high school. But outside of elite colleges that image is less and less accurate in higher education today.

The pool of graduating high school seniors is shrinking as the huge millennial generation ages. Meanwhile, more and more people who didn’t go to college, or who went but didn’t finish, are realizing that their lack of a degree is keeping them from getting ahead. Many of these adult students are veterans cycling out of the military after years of service.

To find out which colleges are best serving this large and growing population of adult students, my magazine, The Washington Monthly, created a ranking of four- and two-year colleges based on adult-specific metrics. We looked at the percentage of a school’s student body that’s 25 and older; tuition charges, student-loan repayment rates and median future earnings; and adult-friendly factors like how many classes are offered on evenings and weekends, when adult students juggling jobs and family responsibilities can actually attend.