What is the author's style in Lemonade Mouth: Adapted Movie Tie-in Edition by Mark Peter Hughes?

The language varies from Charlie's non-standard, very casual language, which is written for a report for a class, and Stella's very sophisticated vocabulary, which adds humor, spice and complexity to the narrative. Stella's, Wen's and Mo's sections make the novel seem more grown up than you would expect from fourteen-year-olds. Charlies sounds about right and Olivia's sections make it sound genuine and heartfelt.