You can be more sure of getting the right answer if you tell us a bit about what part of the book you are asking about. In this case, I just have to guess. I am guessing that you are talking about the part in Chapter 22 right after the trial of Tom Robinson is over.
At that point, Jem is very upset because of the injustice that has been done to his father's client. The morning after the end of the trial, Atticus tells Jem that it is not yet over -- they aren't through. He says this is because Robinson still has a chance to appeal the verdict to a higher court. So Atticus is hoping he might win on appeal.
He's talking about his effort or his work toward Tom Robinson's innocence. Even though at this point the trial is over, he's trying to point out it's not really over. There is plenty of room to appeal, and he makes it sound like he intends to appeal.
He says this at home in front of the family before they learn anything about Tom's experiences in jail.
I think your teacher could also be asking this as a question or pointing out this piece of the text because it might have two meanings. First it has this literal meaning as discussed, but furthermore, it has figurative value. They aren't through fighting for racial equality. This is a piece that has been started by this trial, and in hind sight this book. You could point to our 2008 election as a moment of complete equality.
The passage in To Kill a Mockingbird in which Atticus says this line is very revealing of his character. After he returns from court, Atticus speaks with his sister, Aunt Alexandra, who asks if Jem is all right, commenting that she did not think it wise that the children attend the trial. But, Atticus counters her by replying that Maycomb is their home and they need to cope with the attitudes that exist there. Alexandra says, "Atticus,...you are the last person I thought would turn bitter over this."
"I'm not bitter, just tired. I'm going to bed." Atticus turns in the doorway because Jem stands there and asks, "How could they do it, how could they?" Atticus replies,
I don't know, but they did it. They've done it before and they did it tonight and they'll do it again and when they do it--seems that only children weep. Good night.
This is a rare incidence of Atticus's not having an answer for his children. However, he does not fabricate one or try to "sugar-coat" his response. He again speaks to his son honestly, stating what he perceives as a hard truth. Compassion for men like Tom Robinson comes only from children, implying that only children use their hearts in all judgments. But, lest his children become too disillusioned with life at such a tender age, Atticus is more positive in the morning, reassuring Jem,
It's not time to worry,yet. We're not through yet. There'll be an appeal, you can count on that..."