Must a teacher always laugh?

The job of a teacher is to teach, not to make students laugh, and it's okay not to have a sense of humor. A sense of humor may indeed help in keeping children more engaged in class, but a genuine interest in the students and the subjects being taught, often do just as well. Of course, a teacher may need a sense of humor, not for effective teaching, but just to get through the day - teaching is tough work and often thankless, and a sense of humor may be the only thing that helps maintain sanity on rough days!