In battling an antagonist, the protagonist often experiences personal growth and change. This is true for both Jess and Leslie in their dealings with Janice, the seventh grade bully who torments so many of the littler kids at Lark Creek Elementary. At earlier points in the book, conquering Janice by the power of their wits brings Leslie and Jess closer together, strengthens their self-respect, and saves their reputations in the eyes of May Belle. Like in a fairy tale, Janice is the giant/monster that the physically weak but mentally sharp hero beats through the power of his wits.
Later, though, when Jess and Leslie's fear of Janice is dissolved by seeing her at her most vulnerable – something that can happen for antagonists, but doesn't always – the good friends become even closer as they extend their compassion towards her, where before they had only known to look out for themselves.