"Scout," said Atticus, "nigger-lover is just one of those terms that don't mean anything—like snot-nose. It's hard to explain—ignorant, trashy people use it when they think somebody's favoring Negroes over and above themselves. It's slipped into usage with some people like ourselves, when they want a common, ugly term to label somebody."
This quote is showing how much Atticus values a person being educated about equality. Not only does it show that Atticus is a proponent of racial equality, but it shows that he believes racists are that way because of a lack of education ("ignorant, trashy people").
Another quote is this one: "If you'll concede the necessity of going to school, we'll go on reading every night just as we always have. Is it a bargain?" It's fairly self explanatory in that Atticus is telling his daughter that she needs to stop arguing about the importance of going to school, because it IS important to go to school. Earlier in the same conversation, Atticus comes down a little more forcefully on Scout and her attending school when he says: "... dose of magnesia for you tonight and school tomorrow." He's not attempting to make a deal with Scout like the previous quote. Atticus re-emphasizes his feelings on the school issue when he says, "So to school you must go." At that point in the conversation Scout is using the Ewell family as evidence as why she doesn't need to go to school. Atticus responds with a bunch of reasons, and his decision is still the same. Go to school Scout.