Final answer:
Jem tells Scout not to brag about Atticus at school to avoid conflicts and because he understands the complex social situation in their town, respecting his father's humility.
Step-by-step explanation:
In the novel To Kill a Mockingbird by Harper Lee, Jem discourages Scout from bragging about their father, Atticus, at school. Jem's motivation for this is twofold. Firstly, Jem feels the need to protect his younger sister from engaging in conflicts with other children, which might arise from boasting. Secondly, as Jem matures, he begins to understand the complexity of the social structures in their town of Maycomb and realizes that boasting about their father's abilities might not be met well by everyone given the sensitive nature of the Tom Robinson trial in which Atticus is involved. Jem's protectiveness of Scout and his respect for his father's humble approach to life fuel this advisement against schoolyard boasting.