Greendale Community College is one of many institutions whose students are getting the short end of the higher ed stick. (Justin Lubin/NBC)

Pop quiz: What's the biggest category of college or university in the United States? Is it big public research universities like UC Berkeley or the University of Texas at Austin? Or is it their private equivalents, like Boston University and Brigham Young? Maybe all the small liberal arts colleges, like the University of Mary Washington or St. John's in Annapolis have, between them, the most students.

Correct answer: None of the above. According to Delta Cost Project, the biggest category of schools, by full-time enrollment, is actually public community colleges. In 2010, 4.25 million students were enrolled full-time in community colleges, accounting for a third of the whole full-time student population. And that's not even taking into account the many part-time students who rely on community colleges.

The trouble is that America's community colleges are underfunded and underperforming. While research universities are increasing spending at a rapid pace, community colleges are actually spending less. In 2000, community colleges spent $13,285 per full-time student, in 2010 dollars; in 2010, that was down to $12,667, a 4.7 percent decline. And that was after a 40.7 percent spike in community college tuition, without which that spending decline would have been even more severe.

Now, the Century Foundation has released a major new report that suggests the problems with our community colleges go much deeper than funding problems. It was drafted by a task force chaired by Anthony Marx, the president of the New York Public Library and former president of Amherst College, and Eduardo Padrón, president of Miami Dade College, a former community college that now offers four-year degrees and is the second largest higher educational institution in the United States. The results are summarized in the slides below:

For one thing, the report finds that the socioeconomic divide between community colleges and elite colleges is imposing. Seventy percent of students at elite colleges are in the top 20 percent of the income scale; only 16 percent of students at community colleges are. Meanwhile, only 5 percent of elite college students come from the bottom 20 percent of the income scale, while 28 percent of community college students do.

And the racial divide between the two is growing. White students make up 75 percent of elite college students, and 58 percent of community college students, while black and Hispanic students make up 12 percent of elite college students and 33 percent of community college students. The black and Hispanic share of community college enrollments has shot up since 1994, and the white share has declined; the demographics of elite colleges have barely changed.

That's all especially troubling because the report finds that community colleges are failing miserably at helping students get bachelor's degrees. Of community college entrants, 81.4 percent say they plan on getting a bachelor's degree. Only 11.6 percent end up doing so. Worse still, some of those students likely would have done better had they gone to traditional four-year colleges. The report notes that a federal longitudinal study found that students who graduated high school in 1992 with college-ready math (defined here as trigonometry) were far likelier to get bachelor's degrees if they went to four-year colleges rather than two-year ones. That's especially true for poor students. Sixty-nine percent of those who went to four-year schools graduated, while 19 percent of those who went to two-year schools did:

Now, maybe students who chose two-year colleges were less motivated to start with, so perhaps the results here aren't causal, but they're still sobering.

The report makes a variety of policy recommendations to try to make sure community colleges are sufficiently funded (such as by directing public funds to schools that actually teach poor students rather than selective ones that fail to), making it easier for community college students to graduate (such as by creating hybrid two-year/four-year schools like Miami Dade College or by making it easier to transfer to four-year schools), and encouraging integration at community colleges (such as by creating honors and early college programs that attract high-achieving and middle-class students).

Those recommendations tie in well with another recent report, by Caroline Hoxby and Sarah Turner, that suggested ways to get high-achieving, low-income students to attend elite schools that might serve them better; research by Alan Krueger and Stacy Berg Dale found that the economic benefit of selective schools is greatest for poor students. The work follows up on research Hoxby and Christopher Avery did showing that elite colleges frequently miss on high-achieving, low-income students.

Hoxby and Turner ran a randomized experiment where they sent application fee waivers and information about tuition and the application process to low-income high school students who are in the 90th percentile for the SAT or ACT, and who have an A- GPA or higher. These students were 19 percent likelier to apply to public universities whose students are at their achievement level, 17 percent likelier to apply to private universities at that level, and 15 percent likelier to apply to private liberal arts colleges at that level.