One of the disagreements between Atticus and Alexandra was over Jem and Scout sneaking out to go find Atticus.
This chapter begins right after the incident with the Cunningham mob. Atticus brings the two children home, and Jem is eating a heaping helping of breakfast. Aunt Alexandra is very unhappy that Scout and Jem snuck out.
Children who slipped out at night were a disgrace to the family.
Atticus said he was right glad his disgraces had come along, but Aunty said, "Nonsense, Mr. Underwood was there all the time." (ch 16)
Atticus feels differently about the incident than his sister. He feels that Scout and Jem got an important lesson about people’s behavior, and he is also happy that Scout was able to talk to Mr. Cunningham and bring him to his senses, deflating a very tense situation.
The trial has brought many conflicts to the Finch household. Aunt Alexandra has a very rigid view of behavior, especially children's behavior. She thinks that Atticus exposes his children to too many things they should not see. It is not as much their sneaking out that bothers her, but their continuous involvement in all of the unsavory aspects of the trial.