The mood of Nothing But the Truth is constantly shifting—perhaps because the voices, points of focus, and character perspectives of this drama are also constantly shifting.
When we first meet Philip through his diary entry on March 13th, the mood is initially ecstatic. Philip is thrilled that Coach Jamison has identified him as an excellent candidate for the Harrison High track team. He's also preoccupied dreaming about the upcoming Olympics preparations and his dream of competing in the games.
Within a few passages, however, the book shifts to a focus on Philip's teacher, Mrs. Narwin, and the letter she has composed to her sister. In this letter, she laments that students do not have the same love of literature that they used to, and, in this way, the mood shifts to nostalgia and wistfulness.
The mood becomes contentious when Philip repeatedly disrespects Mrs. Narwin by humming during the National Anthem, irritated when Philip rebuffs Allison on the school bus as she asks why he didn't attend track try outs, and hostile when Philip refuses to apologize to Mrs. Narwin. Regardless of how often the mood changes, the underlying commonality to these shifts is that they are ultimately building tension.