The setting of a small, rural town in the Deep South during the Depression Era clearly indicates an impoverished area.
Such areas were not highly populated--Scout mentions later in the narrative that many of the people in Maycomb County resemble one another and that people do not come to the area.
[Maycomb] grew inward. New people so rarely settled there, the same families married the same families until the members of the community looked faintly alike....
There were no factories as there were in the North, so there were few opportunities for employment. Consequently, new people did not come, and those who lived in Maycomb County were anything but affluent or well-schooled. Children on farms often had to work and help in the fields rather than attend school. When they did attend, they often had to repeat a grade because they had missed so much that they failed. Such is the case with the Cunningham children.
That the one elementary school in this southern part of Alabama hires Miss Caroline from Winston County (to this day, there are those in Alabama who disparage this county for its disloyalty during the Civil War and still have negative feelings for anyone from the area) indicates that this school has difficulty finding teachers. Clearly, there are not enough truant officers and other government officials to keep up with those like the Ewell family since the truant children come only on the first day.
Apparently, there is no kindergarten, so the first grade children know very little about letters or reading, with the exception of the precocious Scout, who has been taught by Atticus. Ironically, Miss Caroline is angered that Scout can read; she thinks Scout has not been taught properly.
Since Harper Lee's novel is set in the Jim Crow South, the school that Scout and Jem attend is for whites only. Any schooling that the black children receive is from whatever is taught to them privately. Because there were few opportunities for black people to learn to read, the congregation at the African Methodist Episcopalian church is illiterate, a fact that shocks both Jem and Scout when they attend with Calpurnia. But Calpurnia explains that she was tutored by Miss Maudie's aunt, Miss Buford, years ago, and she later taught her son Zeebo.