What are four classes of people in To Kill A Mockingbird?

After the arrival of Aunt Alexandra, Scout realizes that there is a caste system in Maycomb: Fine folks, the lower working-class people like the Cunninghams, the white-trash like the Ewells, and the Negroes.

In the Deep South in the 1930's, where there was virtually no industry, so the middle-class did not really develop until many decades later.  There were those of the upper-class who were descended from the property-owners. Then, there were those who were descended from the poorer whites, who used to be the overseers on the plantations, or they were indentured servants. Many of these became sharecroppers after the Civil War; thus, they were lower class. Men like Mr. Cunningham fell into this class. Finally, among white people there were the shiftless and lazy; men like Bob Ewell. Then, there is the underclass of the African-Americans.

It is after Jem talks with his father about the outcome of the Tom Robinson trial and learns that it was Mr. Cunningham who held out on voting against Tom, that he has his insight into the four divisions of people in Maycomb county:

"You know something, Scout? ....There's four kinds of folks in the world. There's the ordinary kind like us and the neighbors, there's the kind like the Cunninghams out in the woods, the kind like the Ewells down at the dump, and the Negroes."