For one, dropout rates for MOOCs are exceptionally high. Dr. Siemens estimates that about 10 percent of registrants in his MOOCs (albeit smaller versions of the high-profile U.S. type) complete the course. Coursera’s Dr. Ng gives figures that are in the same ballpark: of 104,000 students who enrolled in his online machine-learning class last year (an earlier iteration of the Coursera version), 46,000 submitted at least one homework assignment, 20,000 completed a substantial portion of the course and 13,000, or 12.5 percent, passed.