Students at school start saying that Atticus "defends niggers." When Scout asks why, Atticus says he's defending a black man named Tom Robinson. Atticus says he won't win the case, but has to take it in order to keep his integrity. He cautions Scout that people, even their friends, might say dirty things to her, and tells her to keep her head up and avoid fighting. Scout does. It's the first time she's ever walked away from a fight.
Scout and Jem begin to see the prejudice that is as much a part of Maycomb as the kindness they've long known. Atticus teaches both tolerance and courage: he never stops thinking of those who disagree with him as friends, but also refuses to let them stop him from fighting for what's right.
Every Christmas, Uncle Jack comes down to Maycomb from Boston and all the Finch's gather at Finch's landing to spend the holidays with Scout's dreaded Aunt Alexandra and her awful grandson Francis. At Finch's landing, Francis calls Atticus a "nigger-lover." Scout punches him, and Francis claims she hit him for no reason and also cursed at him. Uncle Jack spanks her.
The prejudice against blacks in Maycomb is so strong that even family members blame Atticus for defending Tom.
Back in Maycomb, Scout tells Uncle Jack why she hit Francis, but makes him promise not to say anything because Atticus said she shouldn't fight anyone over the Tom Robinson case. Later that night, Scout overhears Jack telling Atticus he doesn't understand children. Atticus says you have to be honest with them.
Jack learns the same lessons about human dignity and respect that Scout is learning. Jack punished Scout without first "stepping into her skin," so he didn't know she'd acted for good reason.
Then Atticus says the trial will be bad, since "reasonable people go mad when anything involving" a black person comes up. He says the trial will be particularly tough on Jem and Scout.
Atticus understands how prejudice can warp people.