I just googled Khan, and one of the first links was a Washington Post critical critique of its math videos. Just great. Educators are saying it doesn't teach or anticipate cofusion or student misconceptions. If my son's school isn't aware of Khan's flaws, and set him up once a week to do Khan as though it's a magical computer gateway, I think that's misleading.
Different kids have different learning styles. My DD will zone out if someone is teaching something she already knows. With Khan's academy, she could just answer the question, shows her mastery and move on. Only the stuffs that she has trouble with, she would do their video lectures. For the sound of it, your DS may not need a lot of video lectures anyway.
