Towards the beginning of Andrew Clements' Frindle, Nick learns from Mrs. Granger that people have power, power to create the world as they want to see it. Nick learns about creative power when he asks Mrs. Granger who determines the meanings of words, and Mrs. Granger gives the following reply:
Who says dog means dog? You do, Nicholas. You and I and everyone in this class and this school and this town and this state and this country. (p. 28)
After hearing this response, Nick starts thinking about how much power people have to make things happen, to invent brand new things, and decides to wield his power to invent a new word. Similarly to how he invented the word gwagala to mean music when he was two years old, Nick invents frindle as a new word for pen and influences his peers, as well as eventually the entire world around him, to accept that a pen can now be called a frindle.
By the end of the book, at the age of 21, he sees that frindle has been entered in the dictionary as a new word and reads a letter written by Mrs. Granger when he was in the fifth grade. From the dictionary entry and her letter, he learns just how creative genius, like his own, has the power, not just to momentarily influence but to actually permanently change the world around him. More importantly, he learns that the changes he initiates through his own creativity are a good thing and worthy of pursuing.
Likewise, Mrs. Granger learns from Nick that creativity has the power to change the world, just as the dictionary "changes and grows" (p. 86). Furthermore, she learns change can be a good thing, worthy of being accepted.