They and their widowed father move to Southern California to staying in Elle's home; Elle is now a successful lobbyist in Washington, D. Awaiting the girls are a pair of chihuahua dogs, who are the nephews of Elle's chihuahua Bruiser. Their giddiness is cut short, however, when they find out they are going to attend Pacific Preparatory, Elle's alma mater, a private school requiring uniforms.
Upon their first day, after meeting the strict Headmistress Elsa Higgins, who introduces them to Pac Prep's many rules and extensively detailed honor code, Izzy and Annie register themselves and sign for their ID cards, and meet Chris, a scholarship student who is almost immediately smitten with Annie.
They also start off on the wrong foot with Tiffany Donohugh Brittany Curran , the spoiled daughter of a primary funder of "Pac Prep. Annie and Izzy believe Tiffany to be a sweet person, though she dislikes classmates on scholarship.
However, her true colors come out when she embarrasses Annie and Izzy at a formal dance, revealing that they are on partial scholarship at the school. Izzy and Annie rekindle their friendships with the other scholarship students, including Chris Bobby Campo.
Izzy wants to help Chris get closer to Annie, but in several instances, Annie believes Chris to like Izzy. The twins and their friends believe the uniforms are stifling their creativity and they re-style their clothing while still cleverly abiding by the school's rules.
Chris and Izzy are later accused of cheating on a big history test and they all set out to prove the school wrong. Izzy and Annie suspect Tiffany and Justin are behind this and find that Chris and Tiffany have the same backpack that comes with a lock and key; in Chris's locked zipper pocket, he keeps a master-key that opens all doors in the school and was found broken off in the lock their history teacher's office , for his work-studies to help pay off his scholarship.
They discover that the keys and locks for the backpacks are the same, any key will open any lock. On the floor of the teacher's private office, where the answer key to the test is kept, they discover red markings that match the marks that Justin's expensive shoes create.
They conclude that Tiffany told Justin the uber code to access the answers to the test from their teacher's computer. With this new piece of information, Annie and Izzy set to prove Chris and Izzy's innocence.
In student court, Annie poses as Izzy when she is locked in the bathroom by Justin, and defeats her fear of public speaking. Even as Izzy escapes and returns to the court, Annie points out that Justin owns a new cell phone, one that has not yet been released to the public, and could only have been gotten from one person: Justin, who is irritated by noises such as pencils being sharpened and pen clicks, struggles to hold himself together as the supporters of the twins and Chris click their pens.
He finally admits to framing Chris and Izzy on Tiffany's behalf and Tiffany, upon chewing him out for letting "a blonde make him crack", admits to masterminding the whole plot, though she protests that she cannot be punished since her father is a major founder and continuous donor of the school. Despite this, Headmistress Higgins expels them both for their attempt to frame their classmates for theft and cheating, and their numerous violations of the Pac Prep honor code in the process.
At the end of the movie, Annie and Chris dance together at a school dance and Izzy does the same with Brad a secret scholarship student who assisted the twins in student court by ringing Justin's phone.
The twins and their friends have now become popular at Pac Prep. As for Tiffany and Justin, they wind up facing the consequences for their actions as they are apparently cut off from their wealth as punishment from their parents for their crimes and for shaming their families who founded and donated to the school , and are seen boarding a rowdy student-filled bus and being whisked off to public school, much to their horror.