Why does scout fistfight in school, and how does she learn to resist this temptation? How do scout actions reflect a developing maturity?

A boy at school, Cecil Jacobs, teases Scout, saying that her father "defends niggers". Scout will not accept insults about her father and fights Cecil. Later, she asks Atticus what the phrase means, and he explains that he has decided to defend a black man named Tom Robinson, who lives in a settlement behind the town dump. Atticus says many of the town people think he ought not defend Tom because he is black. Scout asks why he's still doing it if people don't want him to, and Atticus responds that if he didn't take the case, he wouldn't be able to "hold up my head in town," represent his county in the legislature, or even tell his children what to do. Atticus explains that every lawyer gets at least one case in a lifetime that affects them personally, and that this one is his. He tells Scout to keep her cool no matter what anyone says, and fight with her head, not her hands.