Frindle

Nick Allen is a fifth grader with a talent for derailing class discussions, and when he tries it on his strict new teacher, Mrs. Granger, by asking where words actually come from, she turns it back on him: an essay on the subject. The assignment backfires on her — Nick comes away with the idea that a word means whatever enough people agree it means, and he tests it by picking up a pen off the street and declaring, from now on, that it's called a 'frindle.'

The word spreads through his class, then his school, largely because Mrs. Granger fights it — she hands out detentions for saying it, which only puts more students in detention together saying it more. The principal gets involved. A family friend arranges to sell frindle-branded merchandise, and the word gets away from all of them, spreading nationally. Years later, grown up, Nick gets a package from Mrs. Granger: a new dictionary with 'frindle' printed in it as an official word, and a letter admitting she opposed it on purpose, because opposition was what would make it stick.

It's a short book — about a hundred pages — built around one clean idea, executed without padding: language belongs to whoever uses it, not whoever's supposed to be in charge of it. The reservation is exactly what makes it work for its intended reader — it's pitched at the age it's aimed at, fifth grade and around there, and an adult reading it alone will see the ending coming a long way off.