Since Harper Lee's novel, To Kill a Mockingbird, is a bildungsroman, the narrative follows the progression of Jem and Scout into maturing adolescents. So, in order to compile the background information that you need for supporting details, you may wish to recall significant scenes as well as quotes from Atticus Finch.
Reading the summaries of the chapters of this novel here at enotes is a good way to begin. Also, perusing the chapters for significant passages is an important part of writing a veritable essay. For instance, after Scout attends her first day of school, she and her father talk. When she tells Atticus that Miss Caroline has said that he has taught her "all wrong" in Chapter 3, Atticus explains "a little trick" of understanding a person. He tells Scout,
"--until you climb into his skin and walk around in it"
then she will understand. He also makes a secret agreement that they will continue to read without Miss Caroline's knowledge so that her feelings will not be hurt. Scout's experience at the reading sessions with Mrs. Dubose also teach her the importance of being fair-minded.
In Chapter 4, when Atticus catches the children reenacting the "legend" of Boo Radley, he scolds them, telling them to "stop tormenting that man." He explains that what the Radley's do is their business, teaching the children to respect others' right to privacy. Concomitant with this lesson, in Chapter 10 Atticus explains how it is a sin to kill a mockingbird when he gives Jem and Scout air-rifles, a lesson which metaphorically applies to Boo and Tom Robinson.
Of course, during the period before the trial and in the actual trial, Scout and Jem learn much from the example of Atticus Finch who says that he has to work to prevent his children from "catching Maycomb's usual disease" and that Tom Robinson deserves a fair trial. His integrity and his valor in the face the threatening mob, gossips, and the invidious Bob Ewell certainly foster the maturation of both Scout and Jem. That Scout arrives at this fair-mindedness is evinced in the last chapter as she stands on the Radley porch and, no longer "looking through a glass darkly" as scripture refers to a myopic viewpoint, Scout perceives the world no longer as a child.