The narrative voice in To Kill A Mockingbird is relatively unique when it comes to narratives addressing racial relations during the Jim Crow era. Scout, the narrator, is a young white girl whose father encourages independent thought beyond the ideological restrictions of her culture.
The Jim Crow South was characterized by a white culture that firmly believed that it was superior to the black culture within the same community. They justified their position through a number of means, including biological, religious, and sociopolitical. Atticus, the narrator's father, does not necessarily believe in the opinions of his culture just because they are the majority opinion. This practice is instilled in his curious daughter, the narrator.
Having such a voice form the narrative allows the reader to be more critical of many of the characters within the novel. It also removes some of the potential alienation and discomfort many readers experience when reading novels set in this era.
Scout being a child has its advantages and its disadvantages. Her openness and curiosity inform the reader with a seemingly less biased perspective on the people and events around her. On the other hand, Scout's perspective on her father and his beliefs is somewhat biased by the childlike idolatry of a parent. As a result, she unquestioningly believes in his decisions and answers to her many questions. A critical reader may well ask why, for a man who places such trust in the justice system and in things being "put right", he never reveals Boo Radley's crime.