You’ve just got settled into your schedule, you know when you have calculus and where you have to go for Geography class. You know who you’re sitting with and who your teacher is, which feels very relaxed and organized. Before the new semester comes and everything changes.
The idea of changing timetables so frequently is very weird for non-Americans, whose timetables only change once a year. To them, it would seem far too confusing and unsettling never to know where you are and when.