Twitterteachers

Watching his videos highlights how little the Web has changed higher education. Many online courses at traditional colleges simply replicate the in-person model—often in ways that are not as effective. And what happens in most classrooms varies little from 50 years ago (or more). Which is why Mr. Khan's videos come as a surprise, with their informal style, bite-sized units, and simple but effective use of multimedia.

Mr. Khan has a vision of turning his Web site into a kind of charter school for middle- and high-school students, by adding self-paced quizzes and ways for the site to certify that students have watched certain videos and passed related tests. "This could be the DNA for a physical school where students spend 20 percent of their day watching videos and doing self-paced exercises and the rest of the day building robots or painting pictures or composing music or whatever," he said.