After finding out that Maggie is upset about missing one of the collectible Happy Little Elves, Homer drives the family to a Texxon station. This leads to Homer continually buying gas to try and win the rare Baby Must Have toy. Failing, they end up driving through the district of town where Marge grew up.
When visiting her old house, Lisa discovers Marge was a top-grade student.
Meanwhile, during a stunt through the poorly-drained school playground, Bart gets the mud all over Nelson. When Nelson goes to punch him, Bart slips and inadvertently kicks him in the face, leading Bart to become the new school bully.
Lisa discovers that Marge's grade plummeted after she met Homer and so aims not to get distracted, by clearing everything in her room out, including her saxophone. Marge finds out and finds out Lisa wants to be nothing like her.
At school, Nelson confronts Bart at the tetherball, where it hits it by mistake and knocks himself over, and in the hall, where he walks into a locker and gets trapped inside.
Lisa finds out about Cloisters Academy, and tries to persuade her parents to let her go. After the principal and Marge discuss Lisa's record, she is offered a scholarship there.
Bart tries to stop Nelson attacking him by making him feel good about himself.
Lisa discovers that she has not been offered a scholarship and that she was only accepted due to Marge offering to do all the school's laundry. Lisa tells Marge that the kids at the school are snobs and she would rather turn out like her than them, but has a sad look when Marge isn't looking and was lying to make her mom happy.
Homer steals a Baby Must Have from the Texxon store to keep Maggie happy.
(FYI - Ominous music playing when Lisa makes the discovery is: Carmina Burana)