I need help figuring what chapter this quote is from in To Kill a Mockingbird: "'Come on Scout,' he whispered, "don't pay any attention to her. Just hold your head high and be a gentleman.'"
This quote appears in Chapter Eleven, about four pages in. The chapter begins with Scout narrating that as she grew older, she and Jem found the courage to go past Mrs. Henry Lafayette Dubose's house. They couldn't get to the business district of Maycomb without passing her house, so although she was a crotchety old woman who made false accusations toward them, they steeled themselves and passed her place. When Jem revealed to Atticus how furious he was toward the old woman, Atticus urged Jem to be calm. He explained that she was sickly and told Jem to "hold your head high and be a gentleman." Atticus practiced what he preached; he always had a kind word for the old woman when he walked past her house on his way home from work in the evenings.
One Saturday after Jem turned twelve, the two children head into town to spend their money. Mrs. Dubose shouts at them for playing hooky, which of course isn't possible since it's Saturday. She then launches into a tirade about Scout's lack of femininity. She tells her she should be wearing a dress and camisole rather than overalls. She predicts that if Scout continues the way she's going, she'll end up waiting tables at the O.K. Cafe, which terrifies Scout. Jem tries to get Scout to ignore the woman by repeating Atticus's words: "Just hold your head high and be a gentleman."
The admonition from Jem is ironic because Mrs. Dubose is scolding Scout for not being a lady, and Jem tells Scout to be a gentleman. It reveals Jem's naïveté about gender roles, and the fact that he's not able to be a role model for Scout in the expected gender roles of their society. One of the main reasons Scout is such a tomboy is that she emulates Jem as her role model. Here Jem, oblivious to any differences between himself and his little sister, passes on the advice he has received from his role model. The scene to this point is a sweet reflection on the Finch's family dynamic. It soon turns ugly when Mrs. Dubose insults Atticus for acting as a lawyer for a black man.
This is Jem speaking to Scout in ch. 11 when they are passing by Mrs. Dubose's house. She is their cantankerous neighbor, and when Scout tries to give her a friendly greeting, she gets the response, "Don't you say hey to me, you ugly girl! You say good afternoon, Mrs. Dubose!"
Mrs. Dubose also criticizes Scout for what she is wearing: "What are you doing in those overalls? You should be in a dress and camisole, young lady! You'll grow up waiting on tables if somebody doesn't change your ways..."
She goes on to accuse both children of ditching school, asking, “Where are you two going at this time of day? ... Playing hooky, I suppose. I’ll just call up the principal and tell him!”
Despite all her criticisms, Jem encourages Scout to "be a gentleman" and to hold her head high and not let Mrs. Dubose get to her. Ironically, moments later, it is Jem who "loses it" when Mrs. Dubose criticizes Atticus for defending "niggers".
Jem, having just developed an even deeper respect for his father after what happened in ch. 10, comes to Atticus's defense by destroying all of Mrs. Dubose's camellias with Scout's baton. This soon earns him the unusual punishment of reading to her in the afternoons.