Separate Vocations

"Separate Vocations" is the 18th episode of The Simpsons' third season.

Synopsis
After taking career aptitude tests (which were scored by a malfunctioning computer), Lisa discovers that the occupation she's best suited for is homemaker while Bart is pegged as a future police officer. Each takes the opportunity to explore their options as Lisa spends the day doing chores with Marge and Bart goes on a ride along with the police. Lisa hates her role and rebels by becoming a troublemaker at school. Police life fits Bart like a glove and he becomes a hall monitor, handing out demerits to his classmates for minor infractions. When Lisa secretly steals all of the teachers' manuals, it's up to Bart and Principal Skinner to figure out who did it. Realizing his sister is the culprit, Bart takes the rap and returns to his life as a bad student and detention regular, while Lisa goes back to playing her saxophone.