There’s an aspect of the student loan debt crisis that few people are talking about now. A large portion of the debt is carried by former students who have nothing to show for it – they failed to complete college, and so don’t even have a college degree (with its increased earning potential) to help them pay off their loans.

What’s more, there’s a big gap in college dropout rates. Poorer students drop out more often than wealthier students. No mystery here; mostly, students don’t complete their degrees because of financial pressures. Scholarships dry up, their credit is maxed and they can’t afford the next semester’s tuition; or they fall into the all-too-common trap of “sitting out a semester to work and save up some money” – and never go back.

Students from higher-income families might avoid those particular pitfalls, but they too drop out of college and are saddled with debt and no degree.

“A new report released Thursday provides a detailed look at the graduation rates of low-income college students,” reports the nonprofit news agency ProPublica. “At many colleges, low-income students graduate at much lower rates than their high-income peers. At the University of Missouri-Kansas City, only 35 percent of Pell Grant recipients graduate college, a rate that is more than 20 percentage points lower than that of their wealthier peers. And at St. Andrews, a liberal arts college in Laurinburg, North Carolina, only 13 percent of Pell Grant recipients graduate, more than 50 percentage points less than students who don’t receive the grants.”

Pell grants are just that, grants, so they don’t have to be repaid. But a student who receives a Pell grant most likely receives other aid, including student loans.

Ben Miller, the senior director for postsecondary education at the Center for American Progress, says colleges should work harder to ensure students complete their degrees.

“Colleges have responsibility to ensure that the students they enroll are well served,” Miller said. “If you’re going to enroll someone, you should do the absolute best you can to graduate them, or else don’t take their money.”

USA Today calls it the “student’s nightmare.”

“Students who took on debt but didn’t complete any degree are more likely to end up behind on student loan payments,” the newspaper reports, citing a recent Federal Reserve survey. “About 16 percent of borrowers who did not complete any degree or certificate report being behind on payments. It jumps to 21 percent of those who have no degree and are no longer enrolled in the program for which they borrowed.”

This is compared to only 6 percent of borrowers who earned an associate degree, and 4 percent of those with a finished bachelor’s degree.

There’s a lot of constructive discussion going on right now about student loan debt.

There’s also a lot of important and encouraging innovation happening (for example, Texas’ “$10,000 degree challenge”).

But let’s not lose sight of those students who are truly weighed down the most by student loan debt – the ones who don’t have a degree to show for it.