“Some of you may discover a wonderful vocation you'd never even imagined. Others may find out life isn't fair, in spite of your Masters from Bryn Mawr, you might end up a glorified babysitter to a bunch of dead-eyed fourth graders while your husband runs naked on a beach with your marriage counselor!”
After taking the Career Aptitude Normalization Test, or CANT test, Lisa finds out she's more suited to be a homemaker, while Bart is more suited to be a police officer. While Bart enjoys his taste of authority, Lisa turns rebellious after being unable to pursue the career she originally wanted. In the end, it is Bart who stops Lisa from following the wrong path and encourages her to keep pursuing her dreams.
After taking career aptitude tests, scored by a malfunctioning computer, Lisa discovers that the occupation she is best suited for is homemaker, while Bart's test show that he should be a policeman. Lisa is heartbroken over the result and at dinner, she complains about the chosen future for her as homemaker. Marge tells her it can't be that bad, but Homer rudely interrupts her and asks Bart of his chosen occupation. He answers as a police officer which makes Homer proud. However, Lisa reveals that she has future dreams of playing jazz music as a professional saxophone player and is determined to prove the test wrong. She consults a music teacher for his opinion and plays her saxophone with passion. Although he is impressed with her skills, he honestly reveals that because she has inherited her father's stubby fingers, she can never be a professional saxophone player. Much to her disgust, Lisa is therefore required by the test to spend the day doing chores with Marge, while Bart goes on a ride-along with the police.
Lisa hates her role as a homemaker and realizing that her future dreams have been shattered, she loses interest in being a good student. Without any motivation to do her best, Lisa quits playing saxophone and becomes a rebellious, sullen delinquent. Bart enjoys spending time with the police, and he even ends up stopping Snake during a car chase.
The next day, a sulky and depressed Lisa comes downstairs for breakfast. Marge warmly greets her for breakfast, but she doesn't bother to do the same. Lisa makes a snippy comment about how bad being a homemaker is. Marge tries to comfort her by telling her that being a homemaker isn't so bad and she can be creative in the kitchen with making meals, like making smiley face breakfasts for the family. Lisa stubbornly tells her not to bother making the effort because no one in the family appreciates it. Marge tries to prove her wrong, but Bart and Homer tear apart their breakfasts that she works so hard on and forgetting to thank her for them. This discourages Marge and proves Lisa right about their lack of appreciation.
When Principal Skinner discovers Bart's new interest in law enforcement, as seen in the arrest of Groundskeeper Willie for burning leaves in violation of the town's clean air laws, he enlists him as a hall monitor. He soon becomes a good student with good grades. Bart starts handing out demerits to his classmates for minor infractions and has order restored to the school, much to the relief of the faculty. Whereas, Lisa has no interest in school work and is a more rebellious and sulky delinquent. She hangs out with rebellious 5th grade girls in the bad girls bathroom (the one her friend, Janey, warned her not to enter). When the girls tries to kick her out, Lisa suggest hocking Skinner off completely by going after his puma pride statue. They take this to heart realizing Lisa knew more of Skinner's weakness than they do and ruin Skinner's puma making him discouraged that there are still some delinquents willing to take him on despite Bart having restored order in the school. Lisa continues being rebellious by makes snippy comments to Miss Hoover, gets sent to Skinner's office for disciplinary actions and her grades drop as a result. The girls are impressed with Lisa's recent bad behavior and offer her a cigarette. Though reluctant to accept, Lisa does and tells them she will smoke it in class.
In bed while impressed with Bart's turn around, Marge is concerned about Lisa's lack of interest in her school work. She also reveals her concern that Maggie will eventually follow Lisa's footsteps in being a delinquent with a lack of interest in school. Homer tells her not to worry about Maggie for now since she is a baby and has a lot of time to chart her own future.
While serving detention for another nasty comment towards Miss Hoover, Lisa secretly steals all of the Teachers' Editions of the schoolbooks and hides them in her locker. This exposes the teachers' lack of education and it's up to Bart to figure out who stole the books. He finds all the books and realizes Lisa is the culprit. Realizing Bart now knows the truth, she slams her locker shut and confesses her part in it. She reveals she was doing all this because she was rebelling against her chosen future as a homemaker after being discouraged from her original dreams. Lisa tells Bart that before he became a hall monitor, he used to enjoy the simple freedom of rebellion. He admits so, but even he had his limits and Lisa is looking at expulsion for it. She agrees and is heartbroken knowing that she will be expelled with her reputation ruined. Skinner is overjoyed that the Teachers' Editions are found, but asks who is the culprit. Before Lisa could speak up and admit to her wrongdoing, Bart takes the blame and returns to his life as a bad student and detention regular.
Before being taken away by a newly deputized hall monitor, Milhouse to Skinner's office to face punishment, Lisa questions why he did this for her and not let her be punished. Bart reveals he didn't want her ruining her own future because she had the talent and brains to do whatever she wanted in life. He encourages her to keep pursuing her future dreams as a professional saxophone player and promises to be there for her when she needs his help ("while borrowing money from her") in the future. Lisa is that touched by Bart's actions, goes back to being a good student and playing the saxophone. As he spends his time in detention, Lisa plays her saxophone outside his classroom to comfort him. Inside while writing on the chalkboard, Bart praises her and believes she has a great future as a professional saxophone player regardless of what others tell her.