In To Kill a Mockingbird, what are examples of Jem being responsible?

Since To Kill a Mockingbird can be considered a bildungsroman, a coming-of-age story, Jem certainly has his moments of immaturity. On the other hand, he learns to be responsible in the instances in which he cares for others or must make up for his immature actions. In chapter 6, for example, Jem and Dill go over to the Radley house to see if they can catch a glimpse of Boo. Unfortunately, Mr. Radley hears them in the backyard and comes out shooting his gun in the air. As the kids are slipping under a fence to get away, Jem's pants get caught, and he has to leave the pants there in order to escape in time. In an effort to cover his tracks, Jem goes back in the middle of the night to fetch them. One might say that this action does not show responsibility because Jem is doing this to avoid getting in trouble. Furthermore, Scout argues that Jem should "take a lickin'" rather than go back to the house and risk death. Jem argues, "Atticus ain't ever whipped me since I can remember. I wanta keep it that way" (56). In his own way, Jem takes responsibility for keeping his clean streak alive and goes after his pants.
Another act of responsibility shows Jem taking care of his sister during Maudie's house fire in chapter 8. For the first few chapters, Jem seems to be either bothered by his sister's existence or at odds with Scout about something else. When a crisis arises, though, Jem steps up and takes care of his little sister without argument. Additionally, he tries to soothe her and keep her calm during the chaos:

Jem put his arm around me. "Hush, Scout," he said. "It ain't time to worry yet. I'll let you know when" (69).

Scout later mentions that her father says the same thing to her when she is scared, so when Jem says it, it helps calm her down. Jem not only knows this, he also puts his arm around his sister to show that he is there for her. This is a great example of taking responsibility on Jem's part.
One more example of Jem taking responsibility is after he attacks Mrs. Dubose's flowers in chapter 11. After freaking out and making a complete mess of an old woman's yard, Jem promptly admits to his father about what he did when he is asked. Jem could have lied or tried to justify his actions to throw all the responsibility on Mrs. Dubose's rude humor, but he does not do that. He looks his father in the eye and admits with complete honesty what he did and why he did it. As a result, he has to go read to the old woman every day for a month. He does this without any prompting from anyone else. Jem takes responsibility for his actions and does not try to hide or justify them. That is a sign of true growth right there.