Final answer:
Atticus is advising an adult to disregard a child's bad behavior as it's simply a phase of testing boundaries.
Step-by-step explanation:
Atticus' statement about "Don't pay any attention to her, Jack. She's trying you out. Cal says she's been cussing fluently this week," reflects a common theme in literature where a child tests the boundaries with a new adult to see how much they can get away with. In this context, Atticus is warning the adult that the child's behavior is not personal but rather a phase of testing limits and experimenting with language as reported by Calpurnia, another character who has insight into the child's recent behavior.