For this novel, you would naturally focus on Jem and Scout as the characters who undergo change, maturation and development as a result of their experiences.
Some specific subtopics relating to the experiences and changing perspectives fro these two characters might be justice, restraint, and expectations.
Regarding justice, both Scout and Jem are forced to adjust their views on how actions are judged in a legal setting and how they are judged in a social setting. The right thing is not always honored, ultimately, and people's prejudices often win.
As witnesses to the events surrounding Tom Robinson’s trial they see a miscarriage of justice, with an innocent man condemned before he even enters the courtroom.
In the events surrounding the trial, including the trial's verdict, Jem and Scout face the realization that their community is not perfect or kind in all its workings. Justice is not to be taken for granted.
The children also learn restraint through their dealings with Boo Radley and Mrs. Dubose. Both these characters help to teach the children to acknowledge the rights and limitations of others and to respect these rights and limitations without automatic judgment.
By the end of the novel, however, eight-year-old Scout has learned a measure of restraint, primarily through the influence and example of her father Atticus.
Also, the children learn to be patient in their perceptions of others because their assumptions and expectations regarding other people are often false in terms of first impressions. This is true with Boo Radley and it is true of Dolphus Raymond.
In both cases, Scout and Jem learn to look past rumor and appearances because these can be deceiving.