What is the climax of Frindle by Andrew Clements?

The climax of a book is the event that all of the earlier tension has led to, the turning point in the story where the action resolves that tension and all of the problems begin to get answered.
In Frindle, by Andrew Clements, the tension revolves around Nick's playful attempt to create a word, "Frindle," which is just another word for "pen." Because words mean what society takes them to mean, as "frindle" becomes more and more widely used in the book, it becomes a more established word. This increases the tension in the story because Nick's teacher, Mrs. Granger, and the school administration fight against the word's growth in order to keep control of their students. Mrs. Granger heads this fight against the word, with her attempts to stomp it out becoming so extreme that local media begins to notice. Of course, this only serves to further publicize "frindle," making it an even more established word.
At one point, Mrs. Granger does a strange thing: She writes a letter, seals it in front of Nick, and tells him to sign it across the back flap to prove it has never been opened.
The climax of the book is the return of this letter. Nick has become wealthy from a trust fund created by his father after he had trademarked the word. Mrs. Granger sends Nick the letter, along with a dictionary that has the word "frindle" in it. The letter tells Nick of how Mrs. Granger had supported him all along, and that she had only fought against the spread of the word to make it grow even quicker.

Andrew Clements's Frindle tells the story of fifth grader Nick Allen and his attempt to create a new word. Nick is inspired to invent a word when he asks his strict English teacher, Miss Granger, where the words in the dictionary come from. When she assigns her students an essay based on the question, Nick uses the opportunity to invent the word "frindle," meaning pen. The word grows in popularity, first with Nick's friends, then throughout his entire school, and soon enough the word is in use throughout his town. His teachers and principal consistently try to stop the spread of the word, but soon realize it is beyond his control.
The climax of the story occurs when Nick's new word becomes so famous that national media outlets begin asking to interview him. This realization inspires Nick's father to sell the rights to the word and invest the earnings in Nick's college fund. Nick's world returns to normal after this; his teachers and school administrators stop trying to punish him and curtail the word, and the national media loses interest as "frindle" becomes a normal term. By the end of the book, "frindle" is a word in the dictionary.