Squirrel (Lucy Punch), switches desks with Halsey (Cameron Diaz), to find out how she obtained the test answers. However, by bringing Halsey's desk into her room she also brings her drugs that were hidden by a false bottom drawer. Halsey knew Squirrel had switched their desks because Halsey spotted a "Learning is FUNtastic" inane sticker on the desk in her classroom, which was not there before Halsey left for Springfield. This was a sticker very prominently displayed on Squirrel's desk, so Halsey figured out the switch was on...and that this was how Squirrel figured out what Halsey did to score the test answer key.
The police arrive at the school with a drug-sniffing dog named Gus and find the hidden drugs, causing Squirrel to have a nervous breakdown as she is hauled off.
The movie closes a month or so later with another end of the year part where Squirrel announces, "I am leaving by my own decision. I have decided for myself, to accept a position at Malcolm X High School in the worst part of the state.” It's clear to all she is being removed from the school and transferred somewhere awful because of the drug bust.
Three months later, Halsey returns to school in her new position as.........the guidance counselor.
Thanks Sean PB!