Imagine that by following a teacher's lesson exactly as she taught it, you could annoy that teacher to no end. Add in the fact that the teacher is exactly the kind of teacher - in students' minds - that needs a little annoying and you've got the situation that Nick has fallen into. Mrs. Granger has told Nick's class that they are the ones who decide what goes in the dictionary. Since they are the ones, along with all other people, who call a dog a d-o-g, then that's what goes in the dictionary.
So Nick gives it a try. He invents the word frindle. Problem is, there already is a word, pen, that describes a frindle. Mrs. Granger is not amused. It's not necessary to invent a word when there already is a perfectly acceptable and usable word, according to "The Lone Granger." So she bans it. Forbids its use. Suddenly fifth graders are staying after school because of the word. Then the rest of the school catches on. (A forbidden word...and it's not naughty? Let me at it!) The students at the local high school hear about frindle. But when a phone call is placed to the local newspaper and a fifth grade class photo - with all fifth graders holding a pen, lips forming the "ffffff" of frindle - mysteriously turns up at the local newspaper, that's when this snowball hits the really steep part of the hill.
Students who stand up for what they think is right even if it's unpopular with teachers, character secrets, a satisfying ending, and a surprise or two along the way make Frindle a winner. Teachers, this is a great one for you if you need a little reassurance that all your hard work does make a difference.