If the MOOC movement were in college, it would be time for a freshman report card. The assessment: great potential, but still in need of remedial work.

MOOCs, or massive open online courses, went mainstream last year, heralded as the next great technological disruption in education. The big idea is that putting lecture videos and interactive course work on the Web will make it possible for top-notch university education to reach more students and allow for different styles of learning.

Already, MOOCs have shown they can attract students in huge numbers. The largest provider, Coursera, has drawn five million, and nonprofit provider edX more than 1.3 million. And while the majority are still based in the U.S., their learners come from all over the globe: Among edX's students, 9% came from Africa and 12% from India.

Big-name schools have also signed on to the idea. Top institutions—from Harvard University to the Massachusetts Institute of Technology to Stanford University—and some companies have joined with MOOC providers to put courses online, free to anyone who wants to access them. Now more schools, to expand their student base and potentially reduce the cost of an education, are building online courses that cost money but offer actual college credit.

For all that great potential, though, MOOCs still have a lot of room for improvement. Early studies highlight a number of problems with the learning experience in online courses that educators are scrambling to solve. Perhaps most important: Staring at a screen makes some students feel isolated and disengaged, which can lead to poor performance or dropping out altogether. Often, more than 90% of people who sign up for a MOOC don't finish, though many come to online learning with a different intent than would students at a traditional university.