Walter Cunningham and Burris Ewell are both from poor families. However, the Cunninghams act with respect and dignity while the Ewells act disrespectfully. On the first day of school Burris is rude, dirty, and badmouths the teacher, making her cry. Walter, on the other hand is quiet, respectful, and refuses to take a handout from the teacher that he knows he cannot repay. Walter has been taught to act honorably. Burris has been brought up in an environment that has taught him to act disrespectfully. He only goes to school on the first day to elude truancy laws. The point Lee makes is that the amount of money a family has does not determine its character.
Burris Ewell and Walter Cunningham both come from poor families who live outside of the town of Maycomb. Burris and Walter also struggle in school because they are absent from the majority of their classes. Both boys dress similarly and are subjected to the same ailments, such as ringworm from not wearing shoes.
Despite growing up in similar economic circumstances, both boys act differently. Walter is shy and respectful, while Burris is loud and rude. Walter also displays his intelligence during his conversation at the dinner table with Atticus while Burris is depicted as an ignorant child. Walter comes from a well-respected, honorable family that lives by a set of moral standards. In contrast, Burris was raised by a malevolent alcoholic and his family is considered a disgrace.
Harper Lee's message regarding the similarities and differences between the Ewells and Cunninghams concerns the importance of a moral upbringing. Despite having similar circumstances, the two boys are raised completely differently. Walter was taught how to properly behave and treat others, while Burris was neglected and followed his father's bad influence.
The only thing that these two characters really have in common is that they are both poor. Walter, for example, is too poor to have a lunch to bring to school.
But they are really quite different, as are their families. Walter is a respectful kid who knows how to behave. He is clean and he is willing to come to school and try to learn. Burris is filthy and lousy and does not care about coming to school.
I think that the author is trying to make the point that people should be judged by their character and not by their economic status or anything else.