Plot

Elizabeth Halsey (Cameron Diaz) is a poor Chicago area teacher who curses at her students, drinks heavily, and takes copious amounts of drugs. She plans to marry her wealthy fiance & hence quits the school where she teaches. But when the fiance dumps her after finding that she is nothing but a gold digger, Elizabeth is forced to go back to her teaching job. She tries to win over substitute teacher Scott Delacorte (Justin Timberlake), who is also wealthy. Their colleague Amy Squirrell (Lucy Punch) is also pursuing Scott, while the school's gym teacher Russell Gettis (Jason Segel - Marshall from How I Met Your Mothere) is making advances on Elizabeth.

Halsey planned on getting breasts implants in order to impress Delacorte but cannot afford the operation. To make matters worse for Halsey, Delacorte begins to have feelings of affection for Squirrell and only views Halsey as a friend. She attempts to raise money for the surgery by participating in her 7th grade class car wash and by manipulating parents of her class students to give her money to take "extra care" of their kids in class, her efforts however were to no avail.

Amy starts by making Elizabeth look bad in front of Delacorte. She tells him about Elizabeth's upcoming fake boobs job. When Delacorte tells Elizabeth that he has feelings for Amy, she tells Delacorte that Amy is just using him for his money. Then Elizabeth joins all the school activities that Delacorte is a part off. She is a hideous person inside, but acts all soft & gooey in front of Delacorte.

She later learns of a bonus for the teacher who has the class with the highest state scores. Halsey decides to change her style of teaching, going from a teacher who only showed movies to one who makes her students study vigorously for the approaching exam. The change in her teaching style and her efforts to prepare her students was not enough, seeing how they were scoring low on the quizzes she gave them. All the while she begins a friendship with Gettis, the gym teacher, and Squirrell and Delacorte begin dating.

Amy finds out that Elizabeth is smoking pot in the parking lot, but since she cant prove it, Principal Snubs decides not to take action. Principal also reminds Amy to keep her emotions under control about Elizabeth & not let them out of control like in 2008 (implying Amy lost it mentally)

Halsey then decides to steal the state exam that her students were going to take by posing as a journalist who wanted to do a report on the racial bias of the exam. When the man in charge of the exams, who she is interviewing, explains he can not give her the exam due to protocol, she resorts to seducing and drugging him in his office and stealing it from his office herself. She also takes nude pictures of him as insurance in case she gets caught. A month later Halsey wins the bonus and pays for the appointment to get her breasts enlarged.

When she hears about a field trip her class is having, and Delacorte and Squirrell will chaperon, Elizabeth puts on a pair of white latex gloves and rubs a poison ivy leaf on an apple and leaves it on Squirrell's desk for her to eat causing her to not be able to go on the field trip and Halsey replacing her. In the field trip she seduces Delacorte and they have sex with their clothes on, which Squirrell finds out through Halsey leaving a 'revealing' voice message on her cell phone. She also gives advice to one of her students on letting go of a crush he has on another fellow student who doesn't like him because she is too superficial, and causing her to reflect for a moment on how she has been superficial as well with her love interests.

After hearing the message, Squirrell switches the desk in her classroom with Halseys' desk in order to get a someone to unlock Eliabeth's desk for her so that she can find evidence that Halsey won the bonus unfairly. She gets the desk opened & finds a clue that points to the person in charge of the exams, who informs Amy that Elizabeth met her in the guise of a reporter & wanted to get hold of the exam prior to them being administered.

Squirrell informs the school principal of what she found in and a meeting is set up for Halsey discuss the matter with the principal and the superintendent. Elizabeth gets away with her mischief through blackmail (using the photos of the man in charge of the tests which she took when he was passed out in compromising positions while she was stealing the test) and informs them that some teachers in the school are doing drugs. (before going to the hearing Elizabeth realized that Amy had switched decks & that meant her drugs were now in Amy's classroom). When the police search the school they find drugs on Halsey's desk which is in Squirrell's classroom and she is thus thought to be the teacher in the school doing drugs. Squirrell is then moved to another school by the superintendent.

With Squirrell gone, Delacorte tries to get sparks going with Halsey. She, however, turns him down due to her realizing that she has a better thing going with Gettis seeing how he is more down to earth and how superficial she has been. The next school year it is shown how Halsey didn't get the breast enlargement because she feels she doesn't need them and she looks fine the way she is, she also seems to be kinder to her co worker, and she started a relationship with Gettis. As well, instead of returning to her English classroom, it is shown that Halsey is now the school's new Guidance Councillor.