"Bart Gets a 'Z'" is the second episode of The Simpsons' twenty-first season. It originally aired on the Fox network in the United States on October 4, 2009. In the episode, 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. In its original airing, the episode had an estimated 9.32 million viewers and received a Nielsen rating of 5.1/8. The episode was written by Matt Selman, and directed by Mark Kirkland.