The biggest problem with this rant is that it's attacking a strawman version of Khan Academy, pretending that it's only a website with some videos and exercises. It's not. KA is actively developing and testing an in-school curriculum that focuses class and teacher time on intensive small group and individual development of the concepts covered in the videos. The main insight is that one-size-fits-all lectures delivered at one pace represents a payment of a large opportunity cost that hurts both ends of the bell curve. If you offload that responsibility to videos that kids can watch outside of class and/or at their own pace, class time becomes an opportunity for kids to work together to understand the concepts and gives teachers the opportunity to figure out how to best reach each individual child. Khan Academy doesn't replace teachers; it frees them up to actually teach.