I actually often "never really intended to seriously take the class in the first place." Coursera doesn't let you view the materials unless you sign up for the class, so I sign up for every class I might be interested in browsing a little. Then I can view the materials at leisure, even long after the class is finished.
On the other hand, I mostly completed the first algorithms course and Model Thinking, and while Daphne's class kicked my ass the first time, I'm already reviewing to tackle it again and try to finish it this time.
It is true though that the time commitment is horrendous, especially for Daphne's class, which estimates 15-20 hours per week! If I fall behind, I may finish slower than their schedule and miss the homeworks and final exam, in which case I'll officially be an incomplete but I'll still have gotten through all the material.
In short, retention is an irrelevant metric for online classes, especially for Coursera which has such a strong incentive to sign up "unseriously." My suggestion would be to keep accepting and grading homeworks and exams at any time, and give extra props on the certs for completing on time with the other students.
On the other hand, I mostly completed the first algorithms course and Model Thinking, and while Daphne's class kicked my ass the first time, I'm already reviewing to tackle it again and try to finish it this time.
It is true though that the time commitment is horrendous, especially for Daphne's class, which estimates 15-20 hours per week! If I fall behind, I may finish slower than their schedule and miss the homeworks and final exam, in which case I'll officially be an incomplete but I'll still have gotten through all the material.
In short, retention is an irrelevant metric for online classes, especially for Coursera which has such a strong incentive to sign up "unseriously." My suggestion would be to keep accepting and grading homeworks and exams at any time, and give extra props on the certs for completing on time with the other students.