The central theme that runs through Frindle is the relationship between power and language. This takes many forms. When Nick asks his patented "thought-grenade" questions, he is trying to get power over how time is spent in the classroom—and, of course, to get out of studying. When Mrs. Granger in turn outsmarts him and refuses to get taken in by the question, she is maintaining control of the classroom through her control of language—and she demonstrates this by assigning Nick an extra oral report, forcing him to bend his use of language to her rules. This question over who will control language, time use, and the classroom finds its purest expression in Nick's creation of the word "frindle."

Nick had not intended to create a new word. In fact, it was only Mrs. Granger treating one of his thought-grenades seriously that led him to do so. When he asked who decides what words have which meanings, she replies, “You do, Nicholas. You and I and everyone in this class and this school and this town and this state and this country." This shows the power a teacher can have over a student: treat a question seriously, and you change the world.

Nick does not do this alone, of course, and much of the novel is devoted to showing how people interact to changes in language. It starts with Nick, spreads to his friends and then to the larger school. Each time the frindle frenzy appears ready to die down, a new language-related force enters. For example, Bud Lawrence produces shirts and pens with "frindle" on them to make money, but when he does so, he also gives the invented word new energy. The same is true of Bud's lawyer (who brings a stack of printed words to Bud to get him to stop promoting his frindle products without Nick's approval), the newspaper reporter (who spreads the story for fun, but feeds it), the television reporter, and so on. Perhaps the most unexpected ways that language and power relate in Frindle are found in the letter Mrs. Granger writes for Nick, but does not give him. In fact, she makes him sign across the seal, so that his unbroken written word will testify to her unbroken promised word not to open it (a very literal power of the word). In the letter, Mrs. Granger reveals that while she had been angry at first, she quickly realized that what Nick was doing was very special—and consciously decided to play the role of the villain to help the story grow. In other words, by fighting frindle, she helped it, showing a subtle understanding of the power of stories, and by doing so, she makes Nick first famous, and then rich.