I presume people are guessing how they are doing by just looking at their homework and midterm scores so far, weighted according to the appropriate weights.
"But in education circles, Mr. Khan’s efforts have captured imaginations and spawned imitators. Two Stanford professors have drawn on his model to offer a free online artificial intelligence class. Thirty-four thousand people are now taking the course, and many more have signed up."
Not sure if "taking the course" means advanced track and completed midterm or not.