The title of the book, Frindle, refers to the name that Nick (Nicholas Allen) decides to use when referring to a simple pen. He is disappointed with having been placed in Mrs Granger's class in fifth grade- she is notoriously strict and well-versed in the correct use of language - and his questions about the origin of words leads him to select "frindle" instead of the word pen, when describing the simple pen. This is Nick's way of trying to gain control in an environment where his teacher is used to being in charge. Nick has always been able to manage his environment but Mrs Granger is quite a challenge. His attempts mean he now has more homework so his plan appears to have backfired. However, he does not underestimate the value of words- Mrs Granger's domain and soon, the name, frindle catches on- much to Mrs Granger's apparent dismay. Everyone refers to a "frindle" rather than a "pen." Mrs Granger's seeming irritation with the use of this word just makes the word, and its usage, all the more popular and the "fad" does not actually "fade." Learners are even prepared to write "this punishment with a pen" if it means they can keep using the word.
Mrs Granger does recognize something in Nick and she is aware of his subtle but smart manipulation of her classroom. She remains resolute in her attempts to stop its use but her very recognition of Nick's talent allows the plot to develop and contributes to the popularity of the word as it becomes a national success.
The relationship between Nick and Mrs Granger changes from one of confrontation to mutual respect. It is Mrs Granger who actually reveals the power of language to Nick and makes him effectively "translate" his obstinate behavior into something useful and particularly powerful without him even realizing it. She is very proud of his achievement when "frindle" makes it into the dictionary.