Both Bill Gates and Sal Khan (and, for good measure, Mark Zuckerberg too) have tried revolutionizing education with technology before. If we look at exactly how and where past attempts went wrong, we might find some challenges for this one too.

I remember when MOOCs were the future of education, as students across the world would have free access to the best lectures from the best teachers and could watch them over and over again at their own pace. That ... didn't result in the second coming of Christ, to put it politely.