Poppy Moore (Emma Roberts) is a seemingly spoiled teenager living in Malibu, California with her father Gerry (Aidan Quinn). In a wild prank with all her friends, she ruins/gives away her father's girlfriend's belongings. Her father returns home and angrily informs her that she is going to an English boarding school to straighten her out.

Arriving at Abbey Mount, Poppy argues with head girl Harriet (Georgia King) and does not get along with the girls in her room. She does not abide by the school rules and sneaks out after lights out. There is a fire drill before she can get back to the room and unknowingly meets the headmistress's son, Freddie (Alex Pettyfer). Later, Poppy and Harriet get into a fight and Freddie flirts with Poppy, making Harriet jealous.

Poppy eventually makes friends with roommate Kate (Kimberley Nixon) and the other girls in the room, who agree to help put together a plan for Poppy to be expelled. After a series of pranks don't get recognition from the headmisstress Mrs. Kingsley (Natasha Richardson), the girls decide that the best way to get Poppy expelled is for her to snog Freddie, who is off limits to any of the girls at the school.

After attending a shopping trip - where Poppy changes her hair from blonde to its natural brunette - and a school disco with the girls in her room, they accept Poppy into their group. The morning after the disco, with the girls hungover, Poppy discovers her talent at lacrosse and is made captain of the school team. She goes on a date with Freddie and realizes that he is more than just a scapegoat. However, her emails were hacked and rewritten by Harriet, then given to the girls and Freddie. She loses her friendships and relationship.

Feeling alone and upset, Poppy plays with her lighter after a phone-call back to Malibu. After hearing footsteps, she accidentally starts a fire, but quickly puts it out. When she returns to her room, she sees the building in flames, supposing the flames were not originally extinguished. She and Kate get everyone out of the school, but Jennifer "Drippy" Logan (Juno Temple) is missing. Poppy remembers Drippy's cravings for ice-cream and runs into the building - forgetting her own safety - and rescues Drippy from the freezer.

Freddie finds Poppy's lighter after the fire brigade extinguish the building and returns it to her, still angry. After an assembly with Mrs. Kingsley, Poppy confesses that she started the fire. After confessing, she sits alone looking at past photos from the school. She notices one picture on the wall and gets upset when she realizes that her deceased mother attended the school as well. Freddie and Poppy apologise to one another and make-up. The honour court is called into session, and the girls realise that it was actually Harriet who wrote the emails. They sabotage the court and Harriet is found out to be the actual cause of the fire, and the cause of the footsteps Poppy heard earlier.

The film ends with Poppy and the lacrosse team in the finals. Poppy's father comes to visit and is taken back by how much she looks like her mother. They win the finals and Poppy celebrates with her father, who is proud of the person she has returned to.

The credits show her friends and Freddie in Malibu with her, declining a call from her Malibu friend, deciding her school friends were better anyway.