How does Jem mature throughout Chapters 12-14 of To Kill a Mockingbird?

In the beginning of Part Two, it is obvious that Jem is
not suffering from a "tapeworm," as Scout suspects. Jem, now 12, is growing into puberty
instead. Later in Chapter 12, Jem gets an education in African-American culture when he
attends the First Purchase Church with Calpurnia. In Chapter 13, Atticus attempts to
give Jem a lesson on "the facts of life." It turns out to be a speech on Aunt
Alexandra's idea of "gentle breeding," and how Finches are expected to behave. Jem
tells Atticus that "I know all that stuff."

In Chapter 14,
Jem learns a great deal from his time spent with Mrs. Dubose. He finds out that
his hot temper can only get him into trouble, and he discovers that he must pay for his
mistakes. Atticus' decision to make Jem read to Mrs. Dubose teaches Jem about respect
for the elderly, and he learns later about the old woman's courageous stand to rid
herself of her addiction before she dies. In the end, after Mrs. Dubose dies and Atticus
presents Jem with a last gift from her, Jem realizes that he has lost a
friend.