<p>Are some classes closed out because seniors hold slots for other students, drop the slot and underclass friend immediately takes that slot? I have heard this happening at some public schools where seniors have priority. It is not allowed, but still happens. Also, I wonder how many slots open up a day before the semester begins when some students take a semester off, change schedules, and change majors. If registration happens online, perhaps one can get into a closed slot if one searches online a couple of times per day a week before classes begin, and a few days into the new semester. Does anyone know?</p>