OK, when the clock hits 1:30, everybody get up, turn your desks around facing to the back of the classroom and sit back down again as if nothing happened.
True story (I'm a retired high school teacher) - one day at the beginning of class, everyone, everyone was standing up and horsing around. They weren't paying one bit of attention to my plea for order. Finally, I said in a loud voice, "Sit down!" They dropped in their spot and sat on the floor in unison.
It was hysterical!
It was staged. The rascals.