Stefan Kühn studies biochemistry at Stellenbosch University in the wine country of South Africa's Western Cape province. He was working on his master's thesis last year and writing in his usual way, which he describes as messy and free-flowing. Then he took a massive open online course (MOOC) from Duke University called Think Again: How to Reason and Argue. It changed the way he approached his thesis. “It taught me what a good argument is, how to construct it, how to avoid general fallacies,” Kühn says. “I started the course because of personal interest (I love a lively debate) and was pleasantly surprised when I realized I was using it for my write-ups as well.”

Kühn enjoys MOOCs and has recommended them to friends, and in this regard, he is typical of many science, technology, engineering and mathematics (STEM) students who take classes from online platforms. A readers' survey conducted by Nature and Scientific American found that more than 80 percent of 1,128 STEM students who had taken at least one MOOC agreed or strongly agreed that they enjoyed the latest course they took. Slightly larger percentages said they would take a MOOC in the future and would recommend MOOCs to others.

Kühn is also typical in that he, like a large majority of those surveyed, did not take the course to fulfill any formal qualification. He uses MOOCs to supplement his knowledge and to learn things he cannot find in his brick-and-mortar university. He followed the Duke reasoning course through to the end but also dabbled in other online courses on social modeling and computer programming. Because the lessons cost him nothing—and do not affect his grades or transcript—he is free to jump in and out as he is able to, without necessarily completing all the assignments or quizzes.

Similarly, Yang Liu, a Chinese citizen pursuing Ph.D. studies at Osaka University in Japan, took MOOCs to fill gaps in her knowledge. Although she had earned a master's in biotechnology, Liu is now doing research on tissue engineering, which she had never studied before. “I didn't have sufficient time to take half-year undergraduate lectures or read [more than] 1,000 pages [of] text books,” she says. So Liu read the transcripts of a Yale University course in biomedical engineering, absorbed the online lecture notes for the Massachusetts Institute of Technology's Molecular Principles of Biomaterials and watched video lectures related to stem cells from other universities. (The Yale and M.I.T. offerings are part of their respective OpenCourseWare programs, which predate MOOCs.) Because her English is weak, Liu could not catch every point in the video sessions, so she had to review lecture notes at the same time. Even so, Liu says, “MOOCs still saved me a lot of time”.

The MOOC students surveyed, nearly half of whom had a biology focus, included skeptics, of course. The number of people who thought traditional courses offered greater educational value than MOOCs was roughly equal to the number who favored the online approach. Yet the percentage of those who thought traditional courses offered superior career value was significantly larger (43 versus 26 percent). Kathleen Nicoll, an associate professor of geography at the University of Utah, took an M.I.T. mathematics class and was underwhelmed. She notes that the course mostly consisted of PowerPoint graphics and canned videos of a professor solving problems. “MOOCs do a good job of basically documenting information,” she says. “It's like television—a very passive experience”.

Although some classes try to mimic research experiences in a virtual lab, that cannot substitute “for smelling formaldehyde or seeing something almost explode in your face and having to react to that,” Nicoll says. She also believes that human interaction is fundamental to learning and that online forums and discussion groups are no substitute. “It's kind of like the difference between having a real friend and a Facebook friend,” she says. Yet even Nicoll sees benefits: “One of the huge upsides is that MOOCs can reach everyone [with a computer and Internet]—people who are differently abled, people behind bars in prison”.

Because failure is cost-free in a MOOC, the basic human tendencies toward procrastination and sloth are stronger than in traditional classes. Still, many STEM students seem motivated to do all or most of the course work, in part to get certificates saying they completed the class. Shannon Bohle, a medical librarian and a blogger at who has taken eight MOOCs, sometimes “lurks” in online classes, but on several occasions she has been driven to do enough work to earn a “statement of accomplishment.” “People always like to have badges and trophies,” she says with self-deprecating humor. “I'm doing the courses as a hobby, really—I'm not applying them toward a degree—and I like to share with my friends that I finished the course and hear everyone say, 'Oh, you're so brilliant. Kudos to you!'”