DAVID EVANS: "Quizzes are part of the lecture to keep students engaged and keep them thinking, for students to be able to check that they understood what we covered. Those are not graded and students try those as often as they want."

They can repeatedly watch the videos and take the quizzes whenever they want.

Students receive homework. They join online groups to exchange questions and answers about the course.

The teachers hold virtual office hours to answer questions that the students have voted to send them. They also present their own questions and observations.

The students take a final examination to show where they rate in the class Everyone who finishes the course receives a grade and proof of completion. Top students get letters documenting their work.

Mr. Thrun started Udacity, which supports free MOOCs. Udacity hopes to make a profit in the future by connecting possible employers with interested students. On his Stanford homepage he says he wants to "democratize" education. Education, he says, should be free, accessible for all, everywhere and any time.

So how does David Evans compare the education in MOOCs to traditional teaching?

DAVID EVANS: "There are things that we can do better in the online format. We can certainly deliver high-quality education to so much more students at much lower cost ."

But he recognizes the limits.

DAVID EVANS: "Part of what I hope will happen as a result of this is that the best traditional universities will be able to focus on the things they can do really well that can't be done better through an online university."