Where does the novel show that Jem is maturing through his actions?

In Part Two of the novel To Kill a Mockingbird, Jem begins to mature into a young man. There are several scenes that depict Jem's maturation through the remainder of the novel. In Chapter 14, after Scout gets an attitude with Aunt Alexandra, Jem tries to tell her that she needs to stop antagonizing Alexandra for the sake of Atticus. Jem is displaying his maturation by understanding his father's growing anxiety due to the upcoming trial, and attempts to discuss his sister's attitude. Jem fails after telling Scout she can't understand Atticus' stress because she "can't hold something in her mind but a little while," and refers to himself as a grown up. Shortly after Scout fights Jem, the children discover Dill has been hiding under Scout's bed. When Dill climbs out from under the bed, Jem tells Atticus. Scout says, "he rose and broke the remaining code our childhood." (Lee 188) By calling his father, Jem displays his maturity because he realizes how serious the situation is. He understands that there are many people concerned about Dill's well-being, and Jem must quickly inform an adult.

In Chapter 15, Atticus travels to the Maycomb jailhouse to sit outside of Tom Robinson's cell. Jem is concerned for his father's safety and decides to go look for him to see if he's alright. When the children arrive at the jailhouse, they see a group of men surrounding Atticus. Scout runs out into the middle of the group, and Jem runs after her. Atticus tells Jem to go home and take the children with him, but Jem refuses to leave. Atticus asks him again, but Jem stubbornly refuses to leave. Fortunately, the mob goes home after Walter Cunningham Sr. realizes the weight of the situation. As Atticus and the children walk home, Scout notices that Atticus is massaging Jem's head, which is a sign of affection. Scout is too young to understand that Atticus is proud of Jem for standing up and refusing to leave. Jem displays maturity by recognizing that his father was in danger and making the bold decision to disobey Atticus' directives.

Following the Tom Robinson trial, where Jem and the children witness racial injustice first-hand and lose their childhood innocence, Jem begins to view situations with a new perspective. At the beginning of Chapter 25, Scout is poking a roly-poly bug and is about to squash it, when Jem tells her, "Don't do that, Scout. Set him out on the back steps." (Lee 317) When Scout asks Jem why couldn't she smash it, he says, "Because they don't bother you." (Lee 320) This scene conveys Jem's maturation in the novel. Jem has witnessed an innocent man, Tom Robinson, lose his life at the hands of a prejudiced community. He understands the importance of Atticus' lesson that it is a sin to kill a mockingbird. Mockingbirds symbolize innocent beings, and Jem knows that the roly-poly should not be harmed because it does nothing to bother anybody. By stopping Scout from squashing the innocent bug, Jem displays his growth and maturation throughout the novel.