We took all 862 videos from four edX courses offered in Fall 2012 and hand-classified each one based on its type (e.g., traditional lecture, problem-solving tutorial) and production style (e.g., PowerPoint slides, Khan-style tablet drawing, talking head). We automatically extracted other features such as length and speaking rate (words per minute). We then mined the edX server logs to obtain over 6.9 million video watching sessions from almost 128,000 students. To our knowledge, this is the largest-scale study of video engagement to date. Here's what we found and a couple recommendations: