In addition to the obvious teaching, it's a teacher's job to command authority at the front of the classroom and keep the troublemakers in line.
It's not always easy for teachers to keep their poker faces on. People on Reddit shared stories of the times the Class Clown or the resident Dumb Kid (who the teacher has to pretend isn't a dumb kid) says something so funny, they couldn't help but laugh.
Me and my buddy sat in front of our strict french teacher. One day while flipping through pages from our french book, I saw a picture of a girl that looked exactly like a classmate that sits 4 seats away from us. My classmate is a guy and if you would to effortless strap a wig on him, he would look exactly like the girl on the book. I then showed my buddy the picture and we began to laugh internally so hard that tears forcefully poured out.
Eventually our teacher took notice and yelled at us, "Would you mind tell the class whats so funny?" We took the opportunity and said, "Alright everyone turn to page 436. You'll see the girl version of William." Everyone completely lost it and even our teacher could not hold herself, but to smile as everyone started cracking up in front of her during lecture. -OrangeKittenGT