Like I said above,... Yes, it is not at all polite to be late/ unprepared. In fact, Like Rick, If I'm not there 30 min. early, & don't call,... something's seriously wrong. I have seen where students have signed up for a class at last minute; I mean within an hour or 2. If the class is not full, then they will be admitted. How are they supposed to read 2 chapters, answer review questions & watch the video? It can't be done. If they've had time,.. to prepare but haven't & are completely lost, then I would seek to help them at a later time or date & in that private setting try my darnedest to get them to be better prepared for the next class, even if it means giving them a "leg up" on the next session. To be honest the late ones don't hold up the class all that much, even though it can be an additional stress on the instructor to get the late one settled in & caught up. If the tardiness is a regular occurrence, I would privately take the student aside & try to see if a middle ground can be found. It may be they get held up at work, traffic is terrible or any number of things. Yes, it would seem to be common courtesy to call if you'll be late (especially with cell phones today), but unfortunately there are some that are clueless about that. Personally I would work to rectify they situation with the student before asking the student to leave the class. It's an extra stress on me, but I prefer to give everyone a second chance.