The Simpsons season 21 episode 2
Episode title: Bart Gets a 'Z'
The fourth grade students of Springfield Elementary School decide to spike Ms. Krabappel's coffee in order to teach her a lesson after she takes away their cell phones. She is fired by Principal Skinner, who hires a new teacher named Zachary Vaughn. Although Vaughn is a hip young teacher who impresses the students, Bart is plagued by guilt and tries to get Ms. Krabappel hired back.