Perhaps the predominant method by which Harper Lee conveys class prejudice is through the use of dialogue. For instance, Aunt Alexandra is the voice for class distinction as she tries to counteract the liberal influence of her brother Atticus by discussing the eminence of the Finches in Chapter 13. Later, he tells Jem,
"Your aunt has asked me to try and impress upon you and Jean-Louise that you are not from run-of-the-mill people, that you are the product of several generations' gentle breeding---"
She is adamant about Scout's not inviting Walter Cunningham to the house, telling her, "...they're not our kind of folks." Further, Aunt Alexandra says,
"That's your father all over again," said Aunt Alexandra, "and I still say that Jean Louise will not invite Walter Cunningham to this house. If he were her double first cousin once removed he would still not be received in this house unless he comes to see Atticus on business. Now that is that."
When Scout asks why, Aunt Alexandra explains that he is "trash." She tells Scout that she does not want him around because Scout will pick up his habits and learn "Lord-knows-what."
Scout and Jem's cousin Francis echoes this kind of thinking,
"Just what I said. Grandma says it's bad enough he lets you all run wild, but now he's turned out a nigger-lover we'll never be able to walk the streets of Maycomb agin. He's ruinin' the family, that's what he's doin'."
That Aunt Alexandra is snobbish comes through with one of Jem's comments to her:
"Aunty," Jem spoke up, "Atticus says you can choose your friends but you sho' can't choose your family, an' they're still kin to you no matter whether you acknowledge 'em or not, and it makes you look right silly when you don't."
Later, Jem explains the class system to Scout, telling her that there is the
ordinary folks 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.
In addition to the use of dialogue as a means of conveying the class prejudices, the actions and reactions of characters also express the distinctions. For instance, while Bob Ewell is on the stand, his reactions to Atticus's questions indicate his sense of inferiority as he misconstrues Atticus's intentions as being to ridicule him. Also, he retaliates against the humiliation that he experienced in court by Atticus's proving him a liar; he spits in Atticus's face in a public place. Thus, through her characterization methods, Harper Lee portrays the class prejudices whether they are real or perceived.
There is an obvious class structure depicted, with the Finches near the top, townspeople below that, uneducated country folks like the Cunninghams even lower, and the white trash Ewells below all the white people. Then, the indication of the black population being even below the sorry Ewells indicates the class structure, including racism and prejudice.
The children don't understand the issue of class, and are constantly questioning it. This, contrasted with the attitude of Atticus that is is a fact of life, but not fair, highlights the idea of prejudice and its injustice.