In Frindle, why is Nick smiling at the end of Chapter 4?
Andrew Clements wrote Frindle in 1996 as an early chapter-book for children, which acts as a transition from picture books and as an examination of the malleability of language.
The main character, Nick, is a smart but unmotivated middle-school student. When he is assigned a report on the origins of words by his teacher, he is initially put off by the sheer scope of the subject. However, because of his rebellious streak, Nick has an idea:
[Nick] covered his eyes with his arm, trying to imagine himself giving a report on all this boring stuff. He'd be luck to have three minutes worth. But because Nick was Nick, he suddenly had an idea and it brought a grin to his face.
(Clements, Frindle, Google Books)
Nick's idea is to filibuster, or draw out his report as long as possible, wasting the teacher's time and allowing the class to get off with a small amount of work. To this end, Nick creates a long speech about dictionaries and their origins, and even reads directly from the boring introduction of the dictionary itself. His plan to waste class time succeeds, but his plan to avoid homework fails; the teacher praises his thoroughness (she figured out what he was doing) and assigns homework anyway.