Would it not be easier just to tell them they failed that class and got a zero in their daily score?? I mean, they are Uni students, right? I don't recall being punished at Uni. If I failed to do my course-work which, essentially, their homework is, I would fail that assignment and if I missed too much course-work, I would not be able to do the exam. Of course, that is not possible to do in China, but just plain telling them that not doing the homework will result in a low or failing grade at the end of the term.