Imagine meeting your English professor by the trunk of her car for office hours, where she doles out information like a taco vendor in a food truck. Or getting an e-mail error message when you write your former biology professor asking for a recommendation because she is no longer employed at the same college. Or attending an afternoon lecture in which your anthropology professor seems a little distracted because he doesn’t have enough money for bus fare. This is an increasingly widespread reality of college education.

Many students—and parents who foot the bills—may assume that all college professors are adequately compensated professionals with a distinct arrangement in which they have a job for life. In actuality those are just tenured professors, who represent less than a quarter of all college faculty. Odds are that students will be taught by professors with less job security and lower pay than those tenured employees, which research shows results in diminished services for students.

Currently, half of all professors in the country are adjuncts or contingent faculty, according to the American Association of University Professors. They teach all levels within the higher-education system, from remedial writing classes to graduate seminars. Unlike graduate teaching assistants, or TAs, they have the same instructional responsibilities as tenured faculty, including assembling syllabi, ordering textbooks, writing lectures, and grading exams. (The remaining quarter or so of American faculty are professors on temporary contracts who have more regular job arrangements than adjuncts, but are not eligible for tenure.)

Adjunct professors earn a median of $2,700 for a semester-long class, according to a survey of thousands of part-time faculty members. In 2013, NPR reported that the average annual pay for adjuncts is between $20,000 and $25,000, while a March 2015 survey conducted by Pacific Standard among nearly 500 adjuncts found that a majority earn less than $20,000 per year from teaching. Some live on less than that and supplement their income with public assistance: A recent report from UC Berkeley found that nearly a quarter of all adjunct professors receive public assistance, such as Medicaid or food stamps. Indeed, many adjuncts earn less than the federal minimum wage. Unless they work 30 hours or more at one college, they’re not eligible for health insurance from that employer, and like other part-time employees, they do not qualify for other benefits.

A year ago, The Atlantic reported on the poor working conditions faced by adjuncts—who, depending on the needs of the school, are often hired a month before the semester begins—beyond their low salaries. To make ends meet, they may teach courses at multiple colleges; they could teach Milton in the morning on one campus and Shakespeare in the afternoon on another. Moreover, according to the analysis, adjuncts are typically excluded from administrative and departmental meetings, meaning they might not be familiar with school policies or other faculty members. On top of instruction, the article explained, they often have to maintain a research agenda and hunt for jobs at faraway conferences without financial support for the trip from a university.

Over the years, the number of tenured professors has dropped while that of adjunct professors has risen, as colleges attempt to rein in costs. Public colleges in particular rely on adjuncts.

Much of these issues have been widely reported on, but what’s often missing from coverage is the impact that this shift is having on students.

It’s unclear whether the transient status and low salaries for adjuncts results in a lower-quality classroom instruction. One 2013 study from the National Bureau of Economic Research found that students in introductory classes with adjunct professors were more likely than those taught by tenure-track instructors to take a second course in the discipline (and more likely to earn a better grade in that course). But Maria Maisto, the president and executive director of the New Faculty Majority Foundation, a group that advocates in the interests of adjunct professors, argued that while many adjuncts are effective teachers, the study’s findings, which were featured in a New York Times report, may be flawed.

Indeed, some suggest that many adjuncts are unable to provide students with the same quality instruction as do tenured faculty. Judy Olson, a longtime part-time professor who currently works as an adjunct at California State University, Los Angeles, acknowledged that her financial concerns sometimes detract time from lesson planning. She cited other adjuncts who she said are unable to maintain independent research that could otherwise enrich classroom discussions. When administrators hire adjuncts only days before the class begins, she added, they can’t properly prepare syllabi and order books.

Adjuncts readily admit they cannot support students outside the classroom, such as when students need extra help understanding an assignment, general college advisement, or a letter of recommendation for a graduate program. And even if they had the time to provide these services, many colleges don’t provide their adjuncts with office space, so they meet with their pupils in coffee shops or at library desks. Olson for her part said that in the past she’s had to meet with students by the trunk of her car, where she kept all her books and papers as she commuted between different college campuses. Without formal meeting spaces, students may find it difficult to locate their professors when they need assistance on their classwork.

Meeting space aside, adjuncts often report that they simply cannot answer common questions from the students about the requirements for the major, course sequencing, or related classes at the college; to get this information, students instead have to track down tenured faculty on campus. Same with letters of recommendation for admission to graduate programs or post-college jobs: Some adjunct professors may not be willing to write them because they aren’t paid for the time, or students may find it difficult to locate former teachers who are no longer employed at that college. Even if they are willing, colleges might not provide adjuncts with institutional letterhead for the recommendations.

These issues are described in research from The Faculty Majority, my interviews with adjuncts, and personal essays, among other sources. Other commentary, meanwhile, reveals the shifting teaching culture at colleges. In a recent op-ed for The New York Times, Mark Bauerlein, a tenured English professor at Emory, argued that students do not have enough interaction with their professors. Professors are no longer “a fearsome mind or a moral light,” Bauerlein wrote. Students simply show up for class, he argued, jump through some hoops, and get their As. Professors are simply service providers and accreditors. He attributed the changing relationship to the pressure on faculty to publish their research and that on students to satisfy competing demands—go to the gym, socialize, and rush for Greek Life, for example.

But various obstacles make it difficult for adjuncts to engage in those traditional relationships, too. Outside-the-classroom responsibilities—office hours, advisement, and recommendation letters, for example—are rarely spelled out in their contracts. These tasks are implicit job expectations, according to Maisto.

Students may not be aware of these behind-the-scenes discrepancies. College brochures and course registration websites don’t distinguish between their adjunct and tenured faculty, and popular college guides and rankings fail to provide adjunct data for specific schools. Olson said, “students don’t know the difference. They think if you teach college, then you’re a professor. They think we make a $100,000 per year.” Maisto echoed Olson’s concerns, arguing that parents are focused on “cost and prestige” and aren’t as focused on quality. Some adjuncts are determined to make this information more transparent with public rallies, crowd sourced data, and walkouts. Both Olson and Maisto also urged that it’s up to students and their parents, too, to include the status of adjuncts in their criteria when shopping for colleges.