What does Atticus tell Scout to do when she hears "ugly talk" at school?
Even though she's still a child, Scout already has some idea of how unacceptable racist language is, especially when it's used to insult Atticus. So, when Cecil Jacobs accuses Atticus of being a "n***** lover" in the schoolyard one day, she doesn't hesitate in using her fists to let him know exactly what she thinks about him.
This is an ideal opportunity for another one of Atticus's life lessons. He tells Scout to keep her head high and her fists down. This isn't just a case of Atticus urging one of his children not to get into fights; his words of wisdom have great practical significance. He knows that the insults that Scout's already received, the "ugly talk," is nothing compared to what she'll hear when the trial of Tom Robinson finally gets underway. Atticus is preparing Scout for what's likely to be a very sudden process of growing up.
When Cecil Jacobs calls Atticus a "nigger-lover", Scout is all too quick to defend her father--by using her fists and beating Cecil into the ground. When Atticus hears about this, he does not scold Scout (in typical Atticus fasion). Instead, he tells Scout that she's probably going to hear some ugly talk at school during the trial. He requests that she keep her head held high and to not use her fists to solve her problems. She does very well with this request until Christmas, when she strikes her cousin Francis for insulting Atticus.
When Scout hears "ugly words" at school, her father, Atticus, says, "you just hold your head high and keep those fists down. No matter what anybody says to you, don’t you let ’em get your goat. Try fighting with your head for a change … it’s a good one, even if it does resist learning.’
Atticus is telling Scout to not give people power over her through her anger, this is what he means about "getting her goat". He saying to her that she shouldn't allow people to make her anger. Also, he tells her to use her mind, not her fists, to deal with her anger and frustration with others. By making this statement, he is also encouraging Scout and pointing out that she has a strong mind and doesn't have to use her fists, which is the easiest response when angered.