Atticus is polite to everyone. He always considers other people's feelings and perspectives. When Walter Cunningham Jr. is eating with Jem, Scout, and Atticus, Scout notes how odd it is to see Atticus treating Walter Jr. like an equal. She is used to hearing adults talk down to children. Atticus does not behave this way:
While Walter piled food on his plate, he and Atticus talked together like two men, to the wonderment of Jem and me. Atticus was expounding upon farm problems when Walter interrupted to ask if there was any molasses in the house.
In talking with Miss Maudie about the history of the Radley family, Miss Maudie notes that it is a sad house, implying that his parents might have been abusive or domineering behind closed doors. Scout replies that her father, Atticus, is the same in public as he is in their home. Miss Maudie agrees completely, saying "Atticus Finch is the same in his house as he is on the public streets." (Chapter 5) Atticus is consistently fair and honest, no matter where he is or who he is with. Scout acknowledges this.
At the end of Chapter 5, Atticus tells the children to stop tormenting Boo Radley. He uses a paraphrasing of the Golden Rule to justify his point. Again, Scout recognizes Atticus's consistency and fairness. Scout narrates what Atticus teaches in this lesson:
How would we like it if Atticus barged in on us without knocking, when we were in our rooms at night? We were, in effect, doing the same thing to Mr. Radley. What Mr. Radley did might seem peculiar to us, but it did not seem peculiar to him. Furthermore, had it never occurred to us that the civil way to communicate with another being was by the front door instead of a side window?