The phenomenon doesn't just apply to videos.

I just read the text, and I didn't see why I should be less optimistic about Khan. What are these studies/tests that show students aren't really learning the science? Remember, Khan does its own tests to check that you learn the material. The relevant question is, are students learning more or less than they would through standard classroom instruction, and is this an artifact of Khan's lesser skill in science teaching specifically, or the entire enterprise of teaching science through a video? Consider that it seems to accept Khan can teach the other subjects just fine...