In part two of To Kill A Mockingbird, Jem is growing up. He and Dill are beginning to enjoy activities in which Scout is not invited. For example, Jem is teaching Dill to swim and Scout is not invited.
Scout is beginning to feel left out. She visits Miss Maudie when she feels down and out.
Also, Jem seems to have less patience with Scout. He is not pleased when she cries. Also, he tells her to act more like a girl.
Calpurnia addresses Jem as mister. He likes his new title, but Scout misses the brother that used to enjoy scoping out the Radley place. Now, Jem is old enough until he no longer believes all the myths about the Radley place. Also, he realizes that life is unfair:
He realizes that right does not always triumph. This is traumatic for a child on the brink of becoming an adult. Jem is, though, fortunate to have the gentle guidance of his father to see past the hypocrisy that seems to surround him. His respect for his father develops in the light of the same events which trouble him.
As Jem matures, Scout is forced to mature as well. She has to accept that Jem is no longer her fond playmate. He is growing into a young man who now views fun and games indifferently.