Students at the Massachusetts Institute of Technology (MIT) are not automatically required to go to class. So you notice when, on a lousy midwinter evening in a driving 45-degree rain, 98 show up at Room 46-3002 in Singleton Auditorium. They come not for the free Thai takeout (though it's appreciated), but because everyone in Eric Lander's introductory biology course is needed. In person.

Ilana Porter, an ebullient first-year student from New Jersey, doesn't mind, and even dumps her plate of noodles to be on time. "We want good seats," she says, and secures a spot in the front row.

Dr. Lander, a MacArthur "genius" and a leader of the Human Genome Project, is the sort of iconic professor you expect to find at the front of a lecture hall at an eminent university. In Ms. Porter's pared down parlance, he is "legit." So much else here, though, is experimental. That's because "Introduction to Biology: The Secret of Life" is also a Massive Open Online Course, or MOOC, offered by edX, the MIT-Harvard University nonprofit, free of charge to anyone in the world with an Internet connection.

Producers film the course with three cameras "like a sporting event," says videographer James Donald. Professional stage lights illuminate the room. Techies with headsets hover at the perimeter. Before Lander, with rain-dampened hair, starts his lecture, he looks to Mr. Donald for the "we're rolling" sign. Then, during more than half the class, he gazes into a teleprompter, addressing a person whose expressive face has been projected onto the screen to make Lander respond to his remote pupils more naturally. Porter and her peers in the auditorium are just the brainy studio audience.

One might ask, exactly whose class is this, anyway?

It's a question arising with increasing frequency from Cambridge to California. Online learning, once considered the Yugo of higher education, is now sweeping through American academia faster than anyone thought conceivable just five years ago. Almost every week, some elite private college or public university announces plans to put professors on camera and beam lectures to students half a mile or half a world away. For the schools, the technology is a way to reach people they might not otherwise engage and to experiment with a tool that could transform how they dispense knowledge in the future.

For those tuning in – often thousands, ranging in age from 9 to 90 – it is a way to brush up on a subject, prepare for a course they may one day take on campus, or just learn from a professor they otherwise would never have access to, like a godfather of the Human Genome Project.

The candid question behind the camera is where this is all leading. Some people, like Harvard Business School professor Clayton Christensen, predict that in as little as 15 years half of the colleges in the United States will be in bankruptcy, upended by online learning and the move to hybrid models in which only select classes are taught in person on campus. Others see more incremental shifts, with virtual learning remaining a tool rather than a transformative technology in higher education.

Yet few doubt that college is ripe for change. Under the current system, students face serious problems getting into and through school, universities struggle to make money, and everyone grapples with fairness issues – why did she get accepted and I didn't? This is to say nothing of the rising cost of a degree that may, or may not, prepare students for a job. Mix in the advent of new technologies such as cloud computing, which makes information, videos, and course work accessible at any time from anywhere, and old-style bricks-and-mortar colleges look ready for reinvention.

Challenges remain on the road to an electronic "edutopia," of course. Traditional universities haven't quite figured out how – or whether – to charge for online courses, or if they should give people credit for taking them. Professors on some campuses are rebelling, concerned that MOOCs devalue in-person teaching. Skeptics argue that digital learning can't provide the intimacy of the classroom or the social experience of the campus.

But some barriers are falling. California is considering a law to require state schools to accept credit for approved MOOCs, in response to more than a half million public college students shut out of oversubscribed basic classes. More broadly, the American Council on Education has recommended five MOOCs as worthy of college credit, which could make it easier to get and transfer courses. The move may lead to putting standardized introductory classes online. Might Lander's course one day be accepted for basic science credit at hundreds of colleges?

Schools are wrestling with more fundamental questions as well. Why would students pay $50,000 a year to trudge through slush for Lander's class when they can get it on their computer screen free of charge? What really is the value of learning on campus? Will the ivy-framed quad even exist tomorrow?

"Disruption is happening," says Anant Agarwal, president of edX, which provides a platform for schools to deliver online courses. "The university, the college, the school as we know it will never be the same again."

* * *

The MOOC is the catalyst behind all the change. It brought the sleepy world of online learning, once perceived as a second-rate alternative, smack into the center of campus.

New online learning models are now surfacing, such as hybrid courses, which combine Internet lectures with in-class teaching. Universities are also forming "closed" networks to offer online courses for credit exclusively to students on participating campuses. The most notable of these, Semester Online, will be launched this fall by a consortium of seven universities on 2U, an educational platform.

While online learning is hardly new, people began seeing it differently after MOOCs went viral in the fall of 2011. Sebastian Thrun, a computer science professor at Stanford University in Palo Alto, Calif., offered his artificial intelligence course free of charge online – and 150,000 people signed up. Soon after, one of his colleagues, Andrew Ng, did the same with his Stanford machine learning course, and 105,000 enrolled. More courses followed. Suddenly, MOOCs were finding audiences worldwide.

Unlike more traditional open courseware – hour-long lectures videotaped from the back of the room and posted on the Internet – MOOCs have caught on in part because they are made for online learning. You can sign up for Lander's course, for example, in just a matter of minutes (the hardest part is devising a clever username). The whole course pops up on the landing page and is easy to explore with the click of a mouse: schedule, syllabus, brief lecture videos, assignments, video "deep dives" explaining topics only touched on in class, discussion forums, and a progress page to track how you're doing.

And you can attend lectures when you want: Watch a lesson now or download it and watch it later. If you missed something, listen to a lecture again. It's all as friendly as a basset hound.

"Welcome back for Week 2," Lander says in a genial tone. Dressed in a blue button-down shirt, he praises everyone for hard work and says the course will only get better. You feel as if he's talking to you, even though he's addressing thousands out in the electronic ether.

"We're done with atoms and bonds, and we're going to move to looking at cool proteins!" he says.

Lander may not be as animated as Bill Nye the Science Guy, but he's close. There is, in other words, nothing scary about this MIT course. In fact, Lander has a special video message urging high school teachers to have their students take it.

The welcoming vibe is classic MOOC, even though online courses exhibit clear differences in style. Some of this stems from the companies that produce them. While more of these educational firms are surfacing every day, three – Coursera, edX, and Udacity – have earned the most attention.

Coursera, a for-profit started by Dr. Ng and Stanford colleague Daphne Koller, reached 1 million users faster than Facebook and is now expanding to become a tool for credit-bearing courses: Ten state university systems recently joined Coursera in a move that could include credit, but is more clearly a bet on using the MOOC platform to increase their reach. EdX is smaller – 27 university partners, 50 courses, and 930,000 students – and has focused more on developing online tools. Udacity, the for-profit started by Dr. Thrun with David Stavens and Mike Sokolsky, has a reputation for strong teaching in math and technology.

While MOOCs are still evolving, they have flourished because they are a mash-up of what many people love: engaging information in video form, gaming, and social networking. In less than a year, they have grown from a handful of courses by a few professors to hundreds of offerings from institutions around the world. Moving tales circulate of people in remote areas whose lives have been changed by free learning from top universities. On campuses, however, MOOCs are less a wondrous new thing than a force unraveling traditions and driving campus leaders to reexamine what it is they do and how they do it.

* * *

On the Tuesday after Memorial Day 2012, Duke University Provost Peter Lange called Lynne O'Brien, director of the college's Center for Instructional Technology, with a simple question: Should Duke begin offering MOOCs? And by the way, he added, we have only about a week to decide.

The university quickly gathered faculty members. Professors wanted in. Duke announced in July that it would partner with Coursera and initially offer eight courses. The first, "Bioelectricity: A Quantitative Approach," began Sept. 24. The instructor, Roger Barr, who looks like Jimmy Carter in suspenders, had taught the same course on campus for 20 years to about 20 to 30 students a semester. Overnight, he was reaching 7,500 from 110 different countries. Dr. O'Brien tracked the MOOC and in February issued a report confirming what other universities have found: Lots of students enroll, but only a handful stick with it. About 300 ended up finishing the class.

This isn't necessarily a sign of failure. MOOCs have more value than the number of people who persevere through the last digital lesson. They offer students more efficient and cheaper ways to learn. The MOOCs track which people watch every video but never bother to take a quiz, helping administrators identify which students are ambitious, which are gifted, and which are merely curious. Even those who only watch a few lectures can glean information: In the Internet Age, after all, most people prefer to buy music by the song, not the album.

O'Brien, in fact, says the Coursera experience has spurred new thinking about campus learning. As professors sought her help, she noticed that no teachers made their MOOC the same length as the standard campus class. "Not a single course is 14 weeks," she says. That raised questions about how content should be broken up. What if a student needs four weeks of a course – but not the whole curriculum?

A more modular approach might help universities tailor courses to the varied backgrounds of their students. Brief online courses in specific areas could help them start on-campus classes at the same level of understanding. "We're going to have things that are not semester-long courses playing a critical role in the curriculum," predicts Dr. Koller of Coursera.

If you start thinking like this, college learning suddenly looks a lot less monolithic. New questions arise: What happens when students arrive having already taken MOOCs? Do they need to take a course with material they've already covered? O'Brien, who recently met with a student who had taken 10 online courses before coming to Duke, says there is now no way to put that on a transcript.

Yet, she says, it "ought to be taken into account. I'd be surprised if we don't have students in the next year saying, 'Well, I took the whole MIT electronics course, and I'd be happy to show you whatever you need to prove it.' "

As more students arrive with online learning in their knapsacks, it could change the direction and duration of their college experience. Students might pivot into research sooner or pursue more advanced courses that enhance their education. Ultimately, it raises the question of whether college needs to last four years. "Why not two or five?" asks Dr. Agarwal of edX. And he wonders: "Is the degree the right currency? I'm not sure."

* * *

Such talk ultimately gets down to the most basic question of all: What is college even for – earning a credential, learning skills, networking, growing up? As important as dispensing knowledge is, O'Brien and others also highlight the value of mentors, peers, and personal growth that an on-campus education provides.

Michael Roth agrees. From where he sits – in the Wesleyan University president's office, a spacious chandeliered room of bookcases, fine English furniture, and arched windows peeking out on a grassy quad – he doesn't believe a campus's tightly knit intellectual environment can be replicated online.

"What we do here doesn't scale up," says Dr. Roth, the Brooklyn-born son of a furrier and the first in his family to attend college. That said, in February Roth began offering his popular campus course, a survey of philosophy, literature, and art, as a MOOC on Coursera. The class size – 27,000 students – "scares the heck out of me," he says, noting the entire Wesleyan campus in Middletown, Conn., has only 3,100 students.

"I'm doing this to find out what the differences are and how we might prepare."

Roth expects more students to arrive ready for advanced work and can imagine "the large lecture going away." He is adamant, however, that students have time to develop intellectually and personally. "I don't want technology to speed up their lives," he says.

Roth is not alone in wanting to preserve the personal feel of college, which is why several top schools formed a network to offer online classes only to students who enroll and are accepted by them. The students will earn credit and pay tuition for the courses. Semester Online will debut this fall, but software engineers at the education platform company 2U are building the features of the virtual classrooms now.

At their offices overlooking the Hudson River in Manhattan, banners adorn cubicles from colleges involved in the electronic venture, including Washington University in St. Louis, Emory University in Atlanta, and Northwestern University in Evanston, Ill. The emphasis will be on small classes – no more than 20 students – and live student-professor interaction.

Students will watch lectures in advance and then "meet" online for classroom discussions. They will stare at screens that look like something from "Hollywood Squares," with each student getting a square. Class members can raise their hands virtually, and no one will be able to do anything without the instructor seeing it.

"You will know all the people in your course," says Chip Paucek, chief executive officer of 2U, dressed in jeans, sweater, and a flowing fringed scarf. "[You] can't go to the bathroom during class without them knowing [you're] gone."

The Semester Online model appealed to Provost Lange because the small classes "convey what is distinctive about institutions like ours" (82 percent of regular Duke classes have no more than 30 students). But months after Duke signed an initial agreement, the Arts and Sciences Faculty Council voted 16 to 14 in April to halt involvement. Lange, surprised by the vote, insists this is a pause, not an end. "I don't see it as a major setback," he says. Advocates like Lange see new online forms as a chance to experiment and learn. But online forays carry costs and payback is uncertain. Will courses become signature offerings and moneymakers with classes offered in multiple time slots to meet demand – or attract only a few?

No one is sure yet what sorts of courses will become standard on Semester Online, introductory or specialized ones, or how this will shape the campus experience. But leaders say online classes are not going away. "When we get it right, teaching some kind of courses online will become second nature to us," says Edward Macias, provost at Washington University. "This puts the challenge in front of us: What do we do in our residential education that we just can't do any other way?"

* * *

While universities wrestle with the promise and problems of the emerging technology, students are attracted to online learning for their own reasons – notably the flexibility and access it provides. Just ask Stephen Conway.

In 2009, Mr. Conway graduated from Nichols College in Dudley, Mass., with a degree in business administration. But he couldn't find a job in an unforgiving economy. So he decided to go back to school at Massachusetts Bay Community College in Wellesley, Mass., to be a computer programmer. Yet he quickly became disillusioned after taking a required introductory course that cost him time and money and offered nothing new. "I wasted a whole class on material I am already familiar with," he says.

Conway, who attends MassBay part time while working full time at The Vitamin Shoppe, also had to redo his schedule when another required course was only offered in the fall. So he was excited when he found out that MassBay and edX were teaming up to offer a hybrid online course that combines an MIT MOOC with on-campus teaching. He signed up right away.

The computer course is taught in a "flipped" format: Students watch video lectures and take online quizzes at home, then come to class, where Harold "Hal" Riggs, a soft-spoken professor with salt-and-pepper hair, helps them puzzle through what they did online. "I'm learning so much more," says Conway.

While elite colleges like Harvard and MIT seem captivated with MOOCs and different online platforms, it is the public universities that may need the technology the most. Public institutions educate three-quarters of the college students in the US, and many of them are having trouble finding enough seats for all those wanting in to their classrooms. At many other places, like MassBay, students juggle work and study schedules. One result is that it often takes people at four-year schools five years or more to complete their degrees.

Yet students are turning to online courses for more than the flexibility they offer. This is evident in Dr. Riggs's class, on a day when the aroma of cafeteria chicken scents the air. Students sit in front of PCs on black-topped lab tables. There is a mixture of pride and bravado in their talk – community college kids doing MIT course work.

Shaunt Keshishian, who balances his studies with a job at a grocery store and freelance Web design work, puts 12 to 14 hours a week into the hybrid course. It's a lot of effort, true, but he likes it because he's learning in a way that works for him. "A traditional classroom lecture doesn't really do it for me," he says. He likes "being able to slow down a lecture, look at it, and take in what [the professor is] saying."

The idea of tailored lessons and quality content is not lost on MassBay President John O'Donnell. He feels pressure from employers to refine what courses the college teaches. "We think in terms of degrees, but business and industry is starting to say, 'Can you credential the skill set?' That is very different than a degree." MOOCs from places like MIT and Harvard offer brand-name content, he says, that interest students and provide consistent quality.

Many, in fact, believe online learning could help ease one of the big tension points in higher education today: the mismatch between what colleges teach and the skills needed in the workplace. They think MOOCs and other online courses will buttress the know-how that's taught on campuses. In other cases, online learning could give students the flexibility they need to get work experience or internships while in college.

Paul Horak, who graduated from Duke last month, was an economics major with a passion for Japanese. He wanted to study abroad during his college years but felt he wouldn't be able to satisfy all his major requirements if he did. How ideal it would be, he says, if one could spend a year in Tokyo and take the required courses at the same time online. "Kids who come after me will be really plugged in," says Mr. Horak, who is taking a MOOC to prepare for medical school. "They will want to have more flexible lives."

* * *

College administrators know this is a different generation. They know the students of tomorrow – and even today – may not have the patience to sit through a long lecture on atoms or anatomy the way earlier students did.

"Forcing students to try to learn at a particular time when class is scheduled," or to focus for a full lecture, may be outmoded, says Ellen Junn, provost of San Jose State University in San Jose, Calif., which has been experimenting with online courses since last fall. "Many people cannot sustain a continued high level of attention for a 50-minute period of time."

In their tinkering with online learning, schools are finding approaches that work. San Jose State, for instance, offers a conventional in-class course on circuits and electronics required for engineering majors. It has suffered from a high failure rate – 40 percent. So last fall the school tried teaching the same course through a hybrid MOOC. The school assigned students randomly to the online course or a traditional one. The failure rate for the MOOC ended up at 9 percent, while students failed the other classes at similar high rates as in the past.

But the online students did a lot more work, spending 10 hours, on average, watching course videos and doing quizzes before coming to class. "That is a very high level of investment," acknowledges Dr. Junn.

Online courses in the future will require adjustments by schools as well as students. San Jose State is offering another class online, entry-level statistics, created by Udacity and two university professors, Ronald Rogers and Sean Laraway. Yet the presenter is 24-year-old Katie Kormanik, a Udacity employee. How will roles change and who will teach tomorrow's classes – traditional professors or a new generation of video-savvy instructors?

Schools will confront innumerable challenges beyond this as they brave the new world of online learning – whether to make classes open to everyone or "closed" like Semester Online; how to award credits; whether to charge for courses and, if so, how much. Many people will be reluctant to pay platinum prices to attend college when they can get the same material on their laptops free of charge.

Others worry that online learning could lead to a two-tiered educational system, with elite schools like Harvard providing content and less selective ones consuming it. In a written statement, some San Jose State faculty objected to increasing the use of MOOCs and online courses, fearing a cheapened educational experience. "Does SJSU really want to be known as Wal-Mart U?" they asked.

Back in Singleton Auditorium at MIT, it seems fitting that Lander's lecture on this day is about Mendelian genetics – about how dominant and recessive traits are passed from parents to offspring. When Gregor Mendel, a European monk, was conducting his experiments in the 1860s, studying 34 varieties of peas, it was not immediately obvious what it meant that he produced two-thirds smooth peas and one-third wrinkled ones.

Similarly, it's not precisely clear where online learning will take American higher education. Will the technology be evolutionary or revolutionary? Will it be lucrative for colleges or bankrupting? Will it be freeing or frustrating for students? For teachers?

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"We have so much to learn about this," says Thrun of Udacity, whose MOOC started the revolution.

In other words, no one knows quite yet what to expect – smooth peas or wrinkled.