Massive open online courses (MOOCs) could help transform education, but face several challenges to realize their full potential. More than 90 percent of students who enroll in a MOOC drop out, as many feel isolated or disengaged. "In large part, the experience is very good, but we see that there are problems, and there are a number of things that can be done that have promise," says edX president Anant Agarwal. "We are not even close to the kinds of conclusions we want." Interpersonal interaction and support help online students to complete courses, and MOOCs are beginning to experiment with different formats to improve the student experience. For example, some instructors record audio comments on assignments instead of writing them to better engage students, or offer motivational messages. Coursera sends students emails to congratulate them on accomplishments and encourage them to reach the next milestone, and Udacity used mentors in trials with San Jose University to coach students and remind them of assignments. In addition, schools are beginning to experiment with "flipped classrooms" that blend online and traditional components, with students watching recorded lectures on their own time and coming into classrooms to work on assignments with the instructor's help.