in the town. And as Aunt Alexandra knows, they often have illustrious roots in the past.

Below them are the deserving poor, such as the Cunninghams. These are people who do without—for example, the Cunninghams can't afford to bring lunches to school—but have pride. They work hard, don't take take handouts, and pay their debts however they can, even if it is through barter.

Next are the white trash, like the Ewells. They are considered lazy and are looked down upon because they don't work hard and instead accept charity. The Ewell children don't go to school. Bob Ewell is an alcoholic, which makes him a blot on the community. Families like the Ewells are isolated and ostracized.

Black people rank below even white trash in the Maycomb social hierarchy. White supremacy is upheld at all costs, and even the most honorable and hardworking Black people are expected to kowtow to lower-class white people. The word of white person is always accepted over the word of a Black person.

Jem tells Scout that there are “four kinds of folks” in Maycomb based on class and race.

The trial’s outcome came as a bit of a shock to Jem.  He was expecting a verdict of “not guilty,” because he believed that Atticus proved Tom Robinson innocent.  When Aunt Alexandra tells Scout that Walter Cunningham is “trash,” Scout is offended.  Jem tells her he understands. 

“… I’ve got it all figured out, now. I’ve thought about it a lot lately and I’ve got it figured out. 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.” (Ch. 23)

To Jem, this social hierarchy is based on who can look down on whom.  The Cunninhams may not have much, but they are better than the Ewells. All the Ewells have is being able to look down on people like the Robinsons, who because of the color of their skin are considered inferior in Maycomb.

Scout is puzzled by the concept that the Finches are superior.  It is important to Aunt Alexandra.  It is not important to Atticus, but he tried to explain it to Scout and Jem to appease her.  She asks why the Cunninhams are not “Old Family” then.  Jem tells her they don’t count. 

“Background doesn’t mean Old Family,” said Jem. “I think it’s how long your family’s been readin‘ and writin’. Scout, I’ve studied this real hard and that’s the only reason I can think of. Somewhere along when the Finches were in Egypt one of ‘em must have learned a hieroglyphic or two and he taught his boy.” (Ch. 23)

The fact that the Finches are from an important family is meaningful to them because, as Jem says, it is all they have.   They do not have a fortune to go with the family name.  They may be respected, but all they have is respect.  They no longer have the power and money to go with the name.

The quote to which you are referring:

You know something, Scout? I've got it all figured out, now. I've thought about it a lot lately and I've got it figured out. 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.

This shows his immaturity, naturally, because he thinks he is superior. As a young adolescent, he is just trying to figure things out for himself, and he has become aware of prejudice all around him. He also realizes that the Ewells are part of the lower hierarchy of society.

If you read Scout's response, you will see that she actually has a more mature grasp of life.

The small town of Maycomb is a microcosm of society in general, with a definite stratification, so to speak, of the population. The idea of social position was very strong in the South during the 30s, almost approaching in dogma the caste system seen in some Eastern cultures today.

The Great Depression, however, "smudged" the permimeters separating the classes, and as seen in the story, trading services in the place of money was a common practice. The court case in question bridged across all social levels as Atticus Finch, a reputed lawyer from an established family, defended Tom Robinson, a poor Negro.

Check out the reference below, an excellent essay treating in depth this subject.

In the first chapter of To Kill a Mockingbird, narrator Scout Finch explains the physical organization of her hometown, Maycomb, Alabama. She begins with her own upper-middle-class, white neighborhood, where she and her brother, Jem, live with their attorney father, Atticus, in a spacious house. The family’s housekeeper, Calpurnia, is African American. In a later chapter, Scout describes going to services in the church to which Calpurnia belongs. The church is located in the Quarters, the African American community where Calpurnia lives, which is on the outskirts of Maycomb. Scout and Jem have never been in Calpurnia’s home.

As the county seat, Maycomb, has a courthouse and public square. It is apparently somewhat larger than other towns in the county. Its downtown includes stores and restaurants. Within the town, less affluent people live farther from the square. There are apparently limited options for middle-class people with limited income, such as teachers. The first-grade teacher boards with the Finches’s neighbor, Miss Maudie.

While Atticus is fully aware of the class divisions among whites, he rarely initiates discussion of these distinctions. His sister, Scout’s Aunt Alexandra, is more vocal; she uses words such as “trash” to label poor white people. Poor families such as the Ewell family live outside the town, past the dump. Even farther out are small farms, most of which are not thriving during the Depression. The Cunningham family farms a small plot, but it is tied up in legal battles over its ownership. There is only one school, located in central Maycomb, to which these children must travel. Scout becomes friends with her classmate Walter Cunningham, but explains that the Ewell children do not attend school.