Out of these three characters, Walter Cunningham and Little Chuck Little are higher than Burris Ewell in social class standing. Chuck isn't seen again in the novel, but it's assumed that he has a tough life, as he "was another member of the population who didn't know where his next meal was coming from." Walter has that same situation, since he doesn't have lunch with him at school, and has no way of paying back a quarter if the teacher was to loan him one. However, one of these boys shows he has manners. Chuck fusses over Miss Caroline after Burris makes a scene and leaves for good. Chuck also shows bravery when he stands up to Burris in class. This scene needed a little hero, and that was Chuck's role.
Walter shows his ignorance of how to conduct himself at the dinner table when he visits the Finch house for lunch. He piles food on his plate, and then covers it with molasses. This only shows how scarce food must be at his house. He does seem as grown up as Chuck, as he is able to hold several adult conversations with Atticus during lunch.
Burris is the perfect definition of white trash. He is dirty, offensive and cruel. He defies Miss Caroline in front of the whole class and even calls her a "snot-nosed slut" as he leaves. He doesn't take care of himself either, since he's the one with the cutie bug.
These three characters are put together to show the difference within similar classes in their society. Although they are all in the same financial situation, Chuck shines as a little gentleman, Walter is the hard working farmer, and Burris is as low as they get. So social classes don't necessarily define who they are in this book. Each character is just as complex as the novel.