Applause

As classes are wrapping up for the semester, many of my classes are closing with the class giving a round of applause for the professor. The first time this happened last year, I was confused and I still am. Is this a common practice at other law schools? In undergrad?
I can’t recall an instance of ending a class with applause at Tufts, although I took many fewer large lecture courses as an undergrad. While teaching a class is a type of public performance, is applause the most appropriate response? Why not applaud at the end of every class session?
We applaud at the end of a symphony, a jazz solo, an opera aria, a lecture, a symposium or after a touchdown, so maybe the custom is not so out of place. Perhaps I’m just not used to the custom, having never seen it at any time that I can remember in my previous 17 years of school.