In her classic novel To Kill a Mockingbird, Harper Lee employed multiple styles of dialect. One could argue that each was chosen to reflect the educational level and cultural background of the character in question. Whites and blacks alike seem to be depicted as having speech patterns consistent with their socioeconomic status.
Lee’s young, precocious narrator, Scout, uses language common to the time, place, level of education, and maturity of this character. The Ewells, the epitome of poor "trash" in Maycomb County, are uneducated, and their speech reflects this. Jem, Scout’s older brother, speaks in the dialect characteristic of the home and town in which he is growing up (“Tom’s jury sho‘ made up its mind in a hurry,” Jem muttered). This is also the case with the African American community in Lee’s fictional town. Reverend Sykes, an educated man of the Bible, speaks articulately. In contrast, Lula, the African American woman who takes exception to the Finch children's presence at a black church, exhibits speech characteristics similar to other characters of a comparable educational level and socioeconomic status (“You ain’t got no business bringin' white chillun here —they got their church, we got our’n. It is our church, ain’t it, Miss Cal?”).
The dialect of other African American characters (most prominently Tom Robinson, but also Zeebo, the kind garbage collector who comes to the Finch children’s aid in the face of Lula’s hostility) appears to be tied to their respective education levels rather than their skin color. (Though it is worth nothing that Zeebo and Tom are both desperately poor and have certainly been denied the educational opportunities offered to white children.) Ultimately, each character’s speech helps us contextualize them within the story—their dialect is reflective of many things, including their socioeconomic status and the region in which they live.