The results of a large study are in. Here’s a review of the results. The upshot: most teachers are just using Khan as a supplement to traditional education. Teachers most commonly used the ability to track student achievements, and used the videos and exercises in small group rotation.
There is a suggestion in this study, though, that more affluent populations (not well represented in the study) may be using more of Khan’s transformational potential. It would be interesting to see more of this aspect.