Just because you're retired doesn't mean your college days are over. Those who miss carting a backpack filled with textbooks and freshly sharpened pencils around campus—but don't miss the tuition—can take free or low-cost classes at many colleges and universities. In some cases, you'll have to meet age, residency, and income restrictions. But with a little research, you just might find yourself writing term papers again. Here's a guide to spending your retirement years on campus without worrying about student loans:

Tuition Waivers. Approximately 60 percent of accredited degree-granting educational institutions offer tuition waivers for older adults, according to a a November 2008 survey by the American Council on Education. But surprisingly, fewer than 50 students at each school that runs such a program utilized it in 2006. The University of North Carolina at Chapel Hill, for example, currently has 21 seniors enrolled in its tuition waiver program, and 30 participated in the University of Virginia's program over the past two semesters. A typical offering is University of Delaware's Higher Education for Senior Citizens, which includes free tuition for degree candidates who are Delaware residents and age 60 or older (the university still charges a variety of fees, however.)

Colleges say one reason more people don’t take advantage of the free tuition is because of the requirements. The waivers often depend on space availability and sometimes require permission from the instructor. And at some colleges, tuition waivers are restricted to credit-bearing courses, while at others only noncredit courses qualify. Some states also have an income cap for eligible participants and require proof of state residency, documentation of retirement, and a high school diploma. Colleges that don’t offer tuition waivers sometimes provide tuition discounts to seniors.

Audit a course. Taking college courses on an audit basis means attending lectures without the homework and exams. Florida residents age 60 or older may audit classes through the Senior Citizen Tuition Fee Waiver program, but they won't receive college credit. “How much work you do is pretty much a negation between you and the teacher you are auditing with,” says Meredith Lobello, 63, a retired computer programmer who is currently auditing two courses at the University of Virginia tuition-free. “I have enough arthritis is my hands that I don’t generally do the written exams,” he says. But Lobello is currently typing a 20-page paper about the history of Iranian cinema for his senior thesis class because he enjoys learning about the topic. “This has been a way of settling into retirement and generally seeing if I can still sit in a room with kids 20 years old and keep up,” he says. Even if your state doesn’t have an official audit program or tuition wavier, it’s worth asking if you can sit in on a class that interests you. Auditing arrangements are often made on an individual basis.

Community college. According to the American Council on Education, about half of college-going adults age 50 and older attend community colleges, primarily for fun, to connect with other people, and to retool for a new career. And 84 percent of community colleges offer courses specifically for students age 50 and older, according to a recent survey of 204 community colleges by the American Association of Community Colleges (AACC). Although not free, community colleges won’t bust your budget. "For a full-time student, the cost of tuition is less than $2,500 dollars,” says George Boggs, AACC president and CEO. “If you break that down by course, it’s less than $800.” National average prices fluctuate by state and college.

Scholarships for seniors. While many scholarships are aimed at traditional undergraduates, it’s worth reading the fine print if you think you might be eligible. Also, be on the lookout for scholarship programs just for seniors. The state of Alabama has a Senior Adults Scholarship Program provides free tuition for senior citizens age 60 and over who are admitted to public two-year colleges in Alabama. And Northern Michigan University offers a full tuition scholarship for applicants age 62 and older, but it doesn’t cover fees or books and online classes are not included.

Living on campus. University-based retirement communities are sometimes located on campus or near campus at schools including Dartmouth College in Hanover, N.H., Oberlin College in Ohio, the University of Florida in Gainesville, and the University of Alabama in Tuscaloosa. Although a spot in an assisted living facility on campus can be quite expensive, many colleges allow residents to attended classes for free and sometimes provide access to college libraries and set aside tickets to sporting events or concerts. Retired Verizon engineer Charlie Klemick, 84, and his wife Ruth, 82, live in an on-campus retirement community at Pennsylvania State University and are both taking an undergraduate course, The Art of Cinema. “We get a great benefit out of associating with the young people, and they allow us to stand up and address the class and give our opinions,” says Klemick. But there's one caveat: “Our class runs at night from 6:00 p.m. to 9:00 and that’s a little long for old people to sit on hard chairs.” Penn State lecturer Jonathan Cavallero, who teaches Klemick’s cinema class, says he enjoys teaching older students because they add to the discussion. “At one point, we were talking about McCarthyism and one of the guys in my class that worked during the Great Depression stood up and talked about how McCarthyism affected him in the 50's and when he was done talking, the students applauded him," says Cavallero. “At times, they become the professors."

Classes for seniors. Some colleges offer continuing education classes specifically for adults age 50 and older. These courses typically last a few weeks instead of an entire semester. In his traditional undergraduate classes and adult classes, Andrew Carle, an assistant professor at George Mason University, presents similar information but leaves more time for questions and discussion with the older students. “When I talk to a group of retirees, hands will be going up all over the place concurrent with the presentation. You don’t see that quite as much from undergraduates or even graduate students,” he says. There is also a network of Osher Lifelong Learning Institutes at approximately 120 colleges and universities in the U.S., including California Polytechnic State University, Texas Tech University, and the University of South Florida. These courses for older adults don’t require papers or exams, and the fees vary considerably by program. At George Mason, for example, the fees range from $125 to $350 annually for an unlimited number of courses over four semesters.

Online courses. Many well-known universities such as MIT, Stanford, and Yale allow anyone to audit select courses online free of charge. Other colleges wave online course fees just for state residents above a certain age. For example, seniors age 65 and older in North Carolina can take public university courses in person, online, or through correspondence for credit without paying tuition. “The online courses are pretty neat because you don’t have to leave the house,” says Peter Rizzolo, 80, a retired doctor who has taken classes both online and in person at the University of North Carolina at Chapel Hill and North Carolina State University on topics including American history, art, and Italian. “I’ve gotten literally thousands of dollar worth of credits—120 or so—for free," he says. "All I’ve paid for is my books and lab fees for courses like astronomy.” Shy students may be more likely to participate in online courses, Rizzolo adds. “Sometimes students are kind of hesitant to open their mouths and afraid to look foolish in class, but online you get time to think about it before you respond.”