Through the semester, I've gotten mildly frustrated by students coming in late to class. Weirdly, the class starts at 2:25pm. And every time, several students are late. I start the class on time, only to be interrupted any number of times by students quietly coming in. They DO try to come in quietly and try not to disrupt; it's not like they're loudly tromping in, calling out to friends. But it's still a disruption.
I went over to another faculty member's place for tea and desert tonight with some other folks, and asked if it was me, if I've lost control or respect or whatever, or if they had the problem, too.
And that's when we figured it out. Most of the classes in this part of the university (the international section) are on even hours/half hours. A class starts at 1pm and ends at 2:20 or so. BUT, my class, since all the students are Japanese, runs on the schedule of the regular university. (Because their classes are spread out geographically, they get 15 minutes between classes. But they still have the same number of minutes in a class, so by the time the afternoon rolls around, the timing between the two sections is way off.)
So my students may be coming from a class that ends only moments before mine begins, so they don't have time to get from one place to the other. Or they're expecting class to start at 2:30, and think I'm just nuts all semester.
I wish I'd known it at the beginning of the semester!
Some things, you don't even think to question. I never would think of a school having two really different schedules.