Landmark research from Carnevale’s center already demonstrates how the post-secondary landscape has evolved into a “separate & unequal” system, as the group calls it. Although far more Hispanic and African American students attend post-secondary schools than two decades ago, most of them have been channeled into the least selective two- and four-year public schools which have the fewest resources to invest in students—and which produce the weakest outcomes in completion or career earnings. Meanwhile, the nation’s 468 most competitive schools remain about four-fifths white, virtually unchanged from 20 years ago, and heavily tilted toward more affluent families. “Right now we have … probably the most stratified college system in the world,” says Margaret Cahalan, vice-president for research at the Pell Institute, which studies higher-education trends.

That powerful sorting shapes not only private, but also public, post-secondary schools. The Georgetown Center has calculated that kids from families earning $106,000 or more comprise 37 percent of all students in “very selective” public colleges while those from families earning less than $30,000 represent only 18 percent. In open-admission public colleges (the least selective schools) the proportions are almost exactly reversed. That matters because on average, the elite schools spend at least twice as much per student as less selective campuses.

Eliminating public university tuition for most families could encourage more low-income young people to pursue higher education by signaling them from a young age that they can afford it, notes Richard Kahlenberg, an expert on college access at the Century Foundation. But tuition-free college, he says, wouldn’t address the principal reasons the top public schools don’t admit more applicants from disadvantaged backgrounds: their fear of falling in national college rankings if they accept students with lower test scores, and their reluctance to invest in the extra support often required to help such students succeed. That’s money, Kahlenberg says, “not spent on reducing class sizes or other things that would increase your national rankings.”

If anything, ending public tuition could compound those problems. Today about two-fifths of kids from families earning at least $106,000 annually attend four-year public schools, and just over one-fifth attend private schools, the Georgetown center calculates. If tuition is eliminated for families earning up to $125,000, many experts consider it inevitable that more upper middle-class families now choosing private schools would shift to public options. And since test scores track closely with parental education, those affluent kids would often arrive with the credentials all colleges covet—leaving less room for students from lower-income districts that don’t produce as many gaudy scores. That’s despite the fact, Carnevale says, that research shows most students with somewhat lower test scores and grades can succeed even at elite institutions with the right support.