Khan tends to follow one textbook from front to back while he goes through the videos in a linear order. The order that khan has his videos listed is the order your supposed to follow in a traditional course. They're small enough so you can go back and brush up on one topic or the next. Each subject topic is one full course, or one that is split into several (like calculus 1, 2 and 3). He has computerized tests for a small amount of topics, and he fills out more and more courses as time goes on. Khan academy is a work in progress.
