Philip Guo, an assistant professor of computer science at the University of Rochester and visiting research scientist at edX, shares preliminary results from an analyses of edX math and science courses that shows students engaged more with shorter videos. He found that the optimal video length is six minutes. He also found that “engagement times decrease as videos lengthen: for instance, on average students spent around three minutes on videos that are longer than 12 minutes, which means that they engaged with less than a quarter of the content.”