Plot
Lizzie McGuire prepares for her junior-high graduation with one of her two closest friends, David "Gordo" Gordon. Their other best friend, Miranda Sanchez, has chosen to skip the graduation ceremony in favor of a trip to Mexico City to visit her relatives. During the ceremony, Lizzie trips onstage and accidentally brings the curtain down on her fellow graduates, which is filmed by her younger brother Matt.
After graduation, Lizzie and her classmates embark on a trip to Rome, chaperoned by their strict future high school principal, Angela Ungermeyer. To their dismay, Lizzie and Kate Saunders are assigned to the same hotel room. While visiting the Trevi Fountain, Lizzie is approached by an Italian pop star named Paolo Valisari, who notices that she bears a striking resemblance to his singing partner, Isabella Parigi.
The next day, Lizzie feigns illness and meets Paolo, who explains that he and Isabella are booked for the International Music Video Awards, but she left Italy after their partnership breakup. He tells Lizzie that Isabella lip syncs and begs her to pose as her for the ceremony. Lizzie reluctantly agrees but soon begins to enjoy the experience and falls for Paolo. Lizzie continues to fake being ill to prepare for the ceremony. Kate finds out and agrees to help her, leading to a mutual friendship. Ms. Ungermeyer grows suspicious, leading Gordo to take the blame and resulting in him being sent back home as punishment.
Matt finds Italian gossip sites with pictures of Lizzie as Isabella. He initially tells his parents he misses Lizzie, convincing his parents to fly them to Rome, during which his parents find out about Lizzie's exploits. At the airport, Gordo meets the real Isabella, who is upset that someone has been impersonating her. The two find Lizzie and warn her that Paolo is planning to have a nervous Lizzie unknowingly sing live at the ceremony, as Isabella actually does, creating the impression that Isabella is a fake, which would damage the latter's career and embarrass Lizzie. The McGuires find Ms. Ungermeyer and reach the award show to find Lizzie.
During the performance, Isabella and Gordo expose Paolo, who is actually the one who lip syncs, by turning on his microphone, revealing his real mediocre singing voice. Upset, he runs off stage, where his displeased manager Sergei resigns, and gets ambushed outside by paparazzi. Isabella introduces Lizzie to the crowd, and the two of them sing "What Dreams Are Made Of".
When Isabella leaves the stage, Lizzie finishes the song solo, displaying a newfound confidence. Later, they celebrate at the hotel's after party, where Ms. Ungermeyer rescinds Gordo's punishment and flirts with Sergei. Although Lizzie's dad tells her she is grounded for the rest of the summer, he says he and her mom are still proud of her. Lizzie and Gordo then sneak away from the party to go up to the roof, where they promise to never let things change between them. They kiss and then rejoin the party.
