By the end of the book, Scout teaches people the importance of seeing things from the point of view of others. Scout, therefore, learns empathy and teaches it to readers. Scout learn this lesson so well that in some way she is Atticus's teacher.
At the end of the book, Atticus wants to follow the letter of the law when it comes to Bob Ewell's attack on his children. In other words, Atticus wants either Jem or Boo to stand trial for the death of Bob Ewell. Heck Tate does not want to go there. He insists that Bob fell on his knife. In this way, everyone benefits. Atticus resists, as he does not see the principle behind it. Scout, on the other hand, sees it.
She sees Boo as a mockingbird. She sees things from his perspective. She, therefore, wants to protect him. Here is the dialogue.
“Scout,” he said, “Mr. Ewell fell on his knife. Can you possibly understand?"
Atticus looked like he needed cheering up. I ran to him and hugged him and kissed him with all my might. “Yes sir, I understand,” I reassured him. “Mr. Tate was right."
Atticus disengaged himself and looked at me. “What do you mean?” “Well, it’d be sort of like shootin‘ a mockingbird, wouldn’t it?”