Farfetch'd, cheesy, and has nothing to do with the show
Lizzie McGuire was a sitcom about a 7th grade girl and her wacky adventures with her friends and family, relying mostly on silly slapstick for its humor, but still being a fairly enjoyable show. The Lizzie McGuire Movie, however, is completely different. Lizzie (Hilary Duff) is graduating middle school and the entire eighth grade is going to Rome (aren't these kinds of things for seniors in high school?). She is quickly spotted out in Italy by singer Paalo (Yani Gellman) as a look-a-like for his singing partner Isabella (also played by Duff). Isabella has left the music world, so Paalo says. Paalo asks Lizzie to pose as her so that he can make a comeback. She agrees while friends Kate (Ashlie Brillault) and Gordo (Adam Lamberg) cover for her to avoid Lizzie getting in trouble with trip leader and soon-to-be-her-principal Ms. Ungermeyer (Alex Borstein) for skipping tours of the city. This is a PG movie and thus fairly predictable, so I think it's safe to say that Lizzie fulfills her dreams of being a singer - which strangely, were never mentioned on the show - without getting in too much trouble.
Generally, this would be a pretty nice idea for a kids' movie. The problem is - this has little to do with the actual show. The show relied on wacky situations to advance its nearly nonexistent storyline. Because of this nonexistent storyline, anything was pretty much possible for the movie. But seriously, having a girl look exactly like you then posing to be her while on a class field trip in Rome so that you can be the world's next big celebrity? Wow, Disney. Just wow.