The film begins with Malcolm (Martin Lawrence) chasing a postal truck, yelling through a loud speaker that he wants his mail. He cuts off the truck and makes the mailman (Ken Jeong) give him his mail. It’s college acceptance day, and he celebrates Trent’s acceptance to Duke (his alma mater), and immediately tries to call Sherry, who’s away at a yoga retreat. He can’t get through, but then gets a call from an informant Canetti about a meeting that’s scheduled that night. He answers a call from Trent (Brandon T. Jackson), who promises to call him back when he’s done at the library. Trent puts away his phone and begins his performance in a park. He spots an attractive girl and raps some lyrics to her, but is interrupted by Malcolm who cuts off the music.
In the car, Trent tells Malcolm that he was offered a chance to tour with some other promising artists, but needs parental permission because he’s underage. Malcolm informs Trent that he’s been accepted to Duke like they’d always wanted. Trent explains that Duke’s always been Malcolm and Sherry’s dream, not his; he has to strike while the iron is hot. Later, Trent gets a call from his friend who suggests that he ambush Malcolm, thinking he’ll sign just to make Trent leave.
Malcolm meets with Canetti and places a wire on him, then checks the flash drive that he’s supposed to give to a Russian gangster named Chirkoff. It’s blank, but he tells Malcolm that he hid it at the Georgia Girl’s School of the Arts, where his friend works. They head to the meeting with Trent following close behind. He approaches Malcolm who’s listening to the meeting from his car. Malcolm yells for Trent to hide when he hears Canetti’s been caught with a wire. A shootout begins. Canetti’s shot from behind by Chirkoff. He falls near Trent and tells him, “It’s in the music “ before being shot by Chirkoff. Trent hides but is caught when his phone starts to ring. Malcolm saves him before Chirkoff can shoot. In the car, Malcolm tells Trent that they have to hide him until they can find the flash drive that will put Chirkoff away for good. When Trent asks where, Malcolm explains.
The next day, Malcolm, disguised as Big Momma, and Trent, disguised as Charmaine Daisy Pierce, arrive at the Georgia Girl’s School of the Arts (GGSA). Big Momma is applying for the newly vacated housemother position, while Charmaine will enroll as a student. They meet with the school’s principal Gail Fletcher (Ana Ortiz), who reluctantly hires Big Momma. She shows them around campus and warns that the girls are pranksters, who possibly stole the mascot of a rival school.
When Big Momma gets to her room, a ballerina named Jasmine gives Big Momma the rundown she makes the rules. At lunch, Charmaine is offered a seat near Haley (Jessica Lucas), who Trent immediately recognizes as the girl from the park. Jasmine tells Charmaine that, as the newbie, she has to perform for the cafeteria. Charmaine gets on the stage and begins to rap. No one seems to be responding, so Haley helps by playing a melody on the piano. She and Charmaine create an interesting duet, which wins over the crowd. As they’re eating, Big Momma comments that Jasmine needs to eat more than just a bowl of peas. One of the girls explains that, as a ballerina, Jasmine can’t be too shapely. Mia, another girl, learns via text message that her boyfriend Delante is breaking up with her. Big Momma tells her to forget him and that it’s better to be alone than with bad company. Principal Fletcher arrives and informs them that a prized music box was stolen and that the culprit will be expelled when caught.
Malcolm realizes that Canetti was trying to tell Trent that the flash drive was in the music box. Big Momma meets with the Director of Operations, Kurtis Kool (Faizon Love), who’s immediately smitten with her, and asks to check the library. He tells her about his suspicion that one of the girls stole it. Big Momma finds a necklace on the floor and takes it with her. Malcolm notices a picture of Kurtis with Canetti and realizes that he’s Canetti’s friend.
Meanwhile, Charmaine is invited to a private party by Haley, who’s being made a DIVA, the most popular group at the school. She promises to never give up on friends or music and is given a necklace. Charmaine asks where Jasmine’s is, and she claims that it’s being repaired. Big Momma breaks up the party. In their room, Trent explains that he’s trying to gain their trust. Malcolm initially refuses the help, but realizes that Trent may be onto something when Trent identifies the necklace as Jasmine’s. They make a deal. Malcolm will sign the contract if Trent helps him and behaves.
Charmaine spends the next day in ballet and art classes. While Big Momma is helping Mia deal with a crisis, Charmaine is invited to go shopping with Haley. They try on clothes and talk boys. Charmaine suggests Haley meet her cousin Trent. Haley is reluctant to meet him because she’s seen how he is when he performs, but agrees to meet him later that night. In the meantime, Big Momma helps Mia fix her hair, which she dyed a horrible red to cope with her breakup. Mia tells Big Momma that she heard Jasmine agree to meet Kurtis later to give him something.
Malcolm stakes out where Jasmine and Kurtis are supposed to meet and bonds with Trent, teaching him a dance called the Cleveland shuffle. Trent sneaks away so he can meet Haley. Things start off rocky, but he manages to convince her to stay. As they walk, they come across his two friends, who call Chirkoff, thinking he’s a music producer trying to sign Trent. Haley brings Trent to the school and plays him a piece she’s been working on. He helps her fine tune it and promises to perform with her at the next night’s showcase. He’s tailed by Chirkoff’s men, but loses them after he changes back into Charmaine.
Malcolm sees the exchange between Kurtis and Jasmine and follows Kurtis back to his apartment as Big Momma. Kurtis flirts and after a game of twister, Malcolm comes clean and demands to know what Jasmine gave him. Kurtis shows Malcolm the mascot of the rival school a rooster, and says that he was going to return for her.
The next day, Big Momma confronts Jasmine and saves her from expulsion, and then has Mia follow Chirkoff’s men, but loses them. At the showcase, Jasmine thanks Big Momma for covering for her, and admits that she had Haley steal the music box as a hazing to join the Divas. She explains that she’s been so mean because she’s hungry and promises to eat a burger after the showcase. Mia stands up to Dilante saying that she doesn’t need him, and she’s over him. Charmaine informs Haley that Trent can’t come. Haley goes on alone, but panics so Charmaine joins her and performs as Trent. Haley pulls off the wig and exposes Charmaine as Trent in front of everyone, including Chirkoff who’s in the audience. Haley runs away. Trent tries to follow but is locked away by Big Momma. Trent escapes and finds Haley in the library where’s she returning the music box. He takes the flash drive and texts Big Momma with their location. He explains that he’s been undercover. Chirkoff’s men ambush them, but they escape with Big Momma’s help. Chirkoff corners them and reveals that he knows Malcolm is Big Momma. He and Trent use the Cleveland shuffle to knock out Chirkoff’s men. They’re almost shot by Chirkoff, but are saved by Kurtis.
The FBI arrive and arrest them. Haley and Trent make up. Malcolm hands Trent the signed tour contract, but Trent tears it after an earlier conversation with Haley made him realize that it might be better to wait. They hug and agree to keep this a secret from Sherry.
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