15-17 would be the optimal student/instructor ratio. In an online format, discussion is essential to both the cultivation of new ideas, but also, the internalization of the information just learned. 15-17 students would allow for the right amount of response opportunities, as well as, a wealth of different perspectives. As an instructor, having 15-17 students would provide the opportunity to receive substantive posts most of the time, and posts that indicate that the student has browsed some of the other view points by other students at other times.