In order to pass a test, Timmy wishes that he knew everything. Timmy's sudden increase in knowledge not only allows him to ace the test but earns him a chair in the Academic Brainathon, replacing AJ. But being a know-it-all has its consequences and we're not just talking about alienating his friends and family. The Brainathon is all about knowing everything and according to the rules, Timmy's braininess constitutes cheating. Timmy's IQ is back to normal but maybe with AJ's intelligence and Timmy's ability to hit the answer button really really fast, the two of them can still win the Brainathon.
Mr. Crocker is handing out the test results to his class. After studying hard, A.J. receives an "A" on his paper, which is decorated with gold stars. One the other hand, Timmy did not study because Cosmo convinced him to play the "not study game" (a.k.a. throw aside his books and play video games). Mr. Crocker hands Timmy an F, soaked in fresh, bloody red ink. Dancing and shaking his butt, A.J. brags about his test score at the lockers to Timmy, and it is seen that A.J.'s locker is full of A's while Timmy's is packed with F's. After A.J.'s seemingly never-ending bragging session, Timmy tells A.J. to knock it off, but A.J. assumes that Timmy is just jealous and that he should study harder. A.J. offers to help Timmy bring his grade up, but Timmy simply scoffs at him. Testing Timmy's knowledge, A.J. smirks and tells Timmy to spell "calculator", and Timmy fails to do so and walks off annoyed. At home, his parents ask Timmy what this F means to them. Timmy says that it's his own fault and he can do better, and his parents sigh in relief because they thought it was their fault and that they would have to blame themselves. After hearing Timmy's "confession", they send him to his room and tell him to work harder.
In his room, Timmy tries to read a book, but he does not even make it past the title of the first chapter before he is overcome by boredom and concludes he is done. Timmy then starts playing the Crash Nebula video game when his phone starts ringing. On the other end of the line is A.J., who hears the video game in the background and tells Timmy that he should be studying. Timmy simply shouts "What are you, my mom!?" and slams the phone down, but puts it down the wrong way and misses the receiver, making A.J. mock him a few more times before Timmy is able to place the phone down right. Infuriated, Timmy rants about A.J.'s superior intellect to his godparents, and then realizes he can just wish to be smarter than A.J. After his wishing that he knows everything, Timmy's cranial cap opens and all the untouched books in the room cram into his head. To test if the wish worked, Wanda poofs them to a gameshow and asks Timmy and Cosmo what the most abundant substance known to man is. Cosmo guesses pudding, while Timmy correctly answers hydrogen and also answers the rest of the questions before Wanda even gave them.
At class the next day, Mr. Crocker is about to give A.J. his usual A, but Timmy steps forward and finishes the sentence Crocker was about to say. He then quickly teaches the class about the Alamo and the state of Texas. Mr. Crocker asks for A.J.'s A and gives it to Timmy as the class cheers, and A.J. shoots a glare at Timmy. At the lockers, A.J. asks Timmy what his scene in class was all about. Timmy says that he is just beating A.J. at his own game and mocks him the same way A.J. did to him earlier. A.J. says that Timmy being smart for a day is no big deal, but Principal Waxelplax walks by and disagrees. She offers Timmy a place on the "Academic Brain-a-thon", first chair. A.J. protests that he always gets first chair, but the Principal assures him he will still get the less important second chair.
At home, Cosmo and Wanda gasp in horror as Timmy begins to mock his parents' intelligence by insulting his dad's spelling and insulting his mom's math abilities, making them reprimand him that he cannot act like a smarty pants. Timmy asks them to prove he was a smarty pants, and then gives a long scientific monologue about the perception of objects in the universe, leaving his parents stunned and his father with a headache. Back at school the next day, the Brain-a-thon is taking place in the auditorium. Timmy and A.J. are seated on one end of the stage, representing Dimmsdale Elementary School, and two other kids sit on the opposite end of the stage, representing Snerd Elementary School. The announcer reads the first question and Timmy quickly presses the buzzer, but as he tries to answer the question, the magic wears off, leaving him to mumble with confusion. The Snerd Elementary kids answer correctly. The next question, Timmy tries to answer again but then runs off, leaving A.J. to answer for him.
His mind blank and empty again, Timmy goes backstage and asks Cosmo and Wanda what was going on. Wanda explains to Timmy that because he is in a competition, Da Rules forbid his magic from being used since that would be cheating. Cosmo and Wanda figured he would know that since he knows everything, but Timmy apparently did not. Back at the Brain-a-thon, Snerd leads Dimmsdale by 8 points. A.J. goes backstage and asks Timmy if he was just faking his stupidity to try making a heroic comeback later on, but Timmy apologizes to A.J. for teasing him even when A.J. earned his intelligence by working for it whereas he cheated to make himself look smart. Forgiving Timmy, A.J. informs Timmy that he is good at video games, and because of this, he has good reflexes on the buzzer. While Timmy is about to reveal to the announcer that he cheated, A.J. asks the announcer to just switch chairs with Timmy, and with Timmy's fast response time and A.J.'s intellect, Dimmsdale's team manages to pull back into the competition.
At the final question, Dimmsdale and Snerd Elementary are tied at 99 points. The final question is one that can be about anything, and to the surprise of them all it is a question about the video game Crash Nebula. Timmy knows he can get this one, and he looks over at one of the Snerd kids, who looks down and reveals he is wearing a Crash Nebula hat. Timmy and the other kid slow motion jump toward their respective buzzers. Timmy reaches his buzzer first, and answers the question in perfect detail correctly. Dimmsdale wins, and Timmy is awarded a golden brain-shaped trophy, which he asks for it to go to A.J. who truly earned it. A.J. lifts the trophy up in triumph, only to promptly drop it on the ground and shatter it.
Back at home, Timmy's parents have hired a lawyer to try to come up with a response to Timmy's smart tirade earlier. Timmy says he deserves to be grounded and admits that he was being a smart creep. The lawyer says Timmy figured it out all by himself and leaves, but he still wants to be paid. Timmy's parents gloat that they grounded a smart kid, and Timmy decides there is nothing left to do but study. He then has Cosmo push away the books and they both hop back into the video game while Wanda huffs in defeat.