|For the minor character, see Karate Girl.|
At Par's karate studio, Carl is well respected by his classmates. As Carl gloats about being star student, Par arrives and tells them that they now have a fourth student: Adelaide. Carl is surprised that she's joining the class, and Par tells him to show her the ropes. Carl intends to use his status to prove why he's the best student, but over the course of the class, it becomes more apparent that Adelaide is more skilled than him, as she excels in everything Par teaches her. When the class ends, Par declares that Adelaide is his new star student, much to Carl's aggravation. Unable to see his status as star student go to someone else, Carl decides to come up with a way to get revenge on her.
In the Casagrande apartment, Carl and Sergio work together to make two kinds of boards: one made of crackers that are easy to break, and one made of rubber that is indestructible. After making the boards, Carl arrives at the Chang apartment to issue a challenge to Adelaide where he says that whoever fails the challenge must quit karate class. Adelaide initially refuses because she's watching a show, but agrees to get him off her back.
Later, at the dojo, Carl and Adelaide are ready for their challenge. As Carl wishes Adelaide luck, Sergio, hiding in his gi, secretly swaps Adelaide's boards with the rubber boards, and while heading back, replaces his boards with the cracker boards. Par tells the two students that whoever breaks more boards within the allotted time will win the challenge, and whoever loses must quit karate class. Once the challenge starts, Carl successfully breaks every one of his boards, while Adelaide can't break a single one. When the time ends, Carl is declared the winner, Adelaide quits the class, and Par, with no other choice, tells Carl he's now his star student and requests his help for a presentation at his school tomorrow.
The next day, as Carl and Sergio carry their new stash of fake boards, Par arrives and tells him that brought some specials wooden boards for the presentation that talk when broken, emit sounds to encourage the crowd to join the studio. Par also reveals in secrecy that the he wants the presentation to be successful, as having more students enrolled will keep it from going out of business (while also revealing that because Adelaide quit, a quarter of the profits have gone away). Realizing he put the fate of the dojo at risk because of his cheating, Carl asks Sergio on what to do now, but Sergio tells him to find another way to cheat and flies off. Peeking in the robotics class, Carl sees Sid working on Breakfast Bot, trying to add a fruit function to him. When Sid leaves to find some more fruit for Breakfast Bot to chop, Carl decides to use that opportunity to steal the robot's arms.
Later, the presentation is about to start. Carl jumps onto the stage, and begins to chop the wooden boards with the help of Breakfast Bot's arms. At the same time, Sid, wanting to test Breakfast Bot's programming on a pineapple, discovers that her robotic companion isn't responding. Fiddling with the remote, Breakfast Bot's arms suddenly start moving on their own, and when she set the controls to max, the arms quickly go haywire. Trying to fight the arms, Carl falls off the stage, revealing his charade to everyone. After Sid takes the arms back, the students are quick to calling Par and the dojo a fraud. When Par declares that his business will be history, Carl speaks up and confesses to the students that he cheated out of jealousy, but Par is a great teacher, and convinces them that Adelaide, who's part of the audience, is the real star. When Carl asks her if she would like to present her skills to save the dojo, Adelaide accepts, saying she was waiting for Carl to admit she's better than him. Adelaide ends up making the presentation a success, and succeeds in motivating the students to join the dojo. When Carl proclaims that he will train harder until he reclaims his position, Breakfast Bot arrives, now with karate programming, and tells him that he'll have to beat him first, much to Carl's fear.