An earlier post on online learning and the future of higher education.
Chronicle of Higher Education: ... Khan Academy is a collection of video lectures that give demonstrations of mechanical processes. When it comes to this purpose, KA videos are, on the average, pretty good. Sal Khan is the main reason; he is approachable and has a knack for making mechanical processes seem understandable. Of course, his videos are not perfect. He tends to ramble a lot and get sidetracked; he doesn’t use visuals as effectively as he could; he’s often sloppy and sometimes downright wrong with his math; and he sometimes omits topics from his subjects that really need to be there (LU decomposition in linear algebra, for example). But on balance, KA is a great resource for the niche in which it was designed to work: giving demonstrations of mechanical processes. ...
This is not to say that Khan Academy can’t play a useful role in learning calculus or some other subject. I don’t deny that mechanical skill is important for getting to the higher-level cognitive tasks. But mechanical skill is a proper subset of the set of all tasks a student needs to master in order to really learn a subject. And a lecture, when well done, can teach novice learners how to think like expert learners; but in my experience with Khan Academy videos, this isn’t what happens — the videos are demos on how to finish mathematics exercises, with little modeling of the higher-level thinking skills that are so important for using mathematics in the real world. So the kinds of learning objectives that Khan Academy videos focus on are important — but they’re not enough.I tried out a couple of Khan Academy videos on my kids recently and I thought they were reasonably effective. Khan is not as precise as a real math professor but he gets the message across.
Small nitpick: he referred to negative numbers as "smaller" than positive or less negative numbers (e.g., -100 is "smaller" than 1), which is I think confusing and even a bit misleading. I think he should have used "less than" rather than "smaller". If you are familiar with complex numbers then you'll probably tend to think in terms of a magnitude (big vs small) and an orientation (with negative numbers along the theta = pi direction), so that -100 is not really small (in magnitude) relative to 1. Presumably Khan learned complex analysis at some point in his education (although maybe not, he went to MIT ;-) IIRC he started out wanting to do physics.