Lisa is failing gym. To make up the grade, she joins a pee-wee hockey league. Soon, her team must face off against Bart's, putting them in direct competition.
Because of impossibly low test scores, Principal Skinner starts to give out academic alerts so the children's parents can understand they are doing poorly. After the series kids receive their alerts, Lisa is called up, surprising everyone. It is then revealed that she is failing gym. Lisa, terrified, goes to her PE teacher and is told to join a Pee-Wee team outside of school. After a sequence of failed attempts at sports, Lisa finally joins a hockey team sponsored by Apu—which just happens to be Bart's rival team. Bart accidentally defeats Milhouse, beats Milhouse up and ties Milhouse to a net. Having talent in hockey similar to Bart's own, she helps turn his team around and Homer starts paying more attention to Lisa. Bart is not happy about the lack of attention and more so when Marge tries to hang out with him.
After Lisa excels at both sports and school, Bart thinks he must become a scholar. This doesn't work out, as he has been a slacker in school for/in his life that is awful. After class, Nelson and his friends confront Bart and prepare to bully him by beating him up and accusing him of wasting Mrs. Krabappel's time. He is inadvertently saved by Lisa who scares off the bullies and instead of being grateful, he accuses her for stealing Homer's affections away from him. Kids laugh at Homer and accuse him of wasting teachers' valuable time. This leads to a rivalry between the entire family, which Marge is less then pleased about, having tried to keep the peace with them and arouses Homer.
When Lisa and Bart play each other, Marge berates Homer for his behavior. He tries to defend himself, but she isn't in the mood and thinks he is a selfish father for starting the rivalry. Homer tries to get her to choose a side, but Marge asserts herself and tells him that she loves all three of their children regardless. She tells him that when they get home, Homer is going to be sleeping on the couch. The game gets down to the wire, with the stadium split between Bart fans and Lisa fans, while Marge is the only one maintaining neutrality. However, when Bart is chosen to take the penalty shot against Lisa, the goalie, they both reminisce about how they helped each other as younger kids (Lisa giving Bart a bandage after he falls off his skateboard, Bart giving Lisa one of his scoops of ice cream when her own falls on the ground). Lisa and Bart throw their hockey gear on the ice and hug. Homer then remarks that they are both losers and the stadium erupts into a riot. Marge is proud of Bart and Lisa, while a despondent Homer turns his attention towards Maggie.