These two classmates of Scout's are some of the poorest in town, yet their differences are evident even from the way they present themselves:

Walter Cunningham is from a family who takes pride in being hardworking and honest. When Walter's father needed Atticus's legal expertise, he insisted on repaying him in the only way he was able: firewood, hickory nuts, and greens. Walter shows up for school clean and with a clear sense of self-respect:

Walter Cunningham’s face told everybody in the first grade he had hookworms. His absence of shoes told us how he got them. People caught hookworms going barefooted in barnyards and hog wallows. If Walter had owned any shoes he would have worn them the first day of school and then discarded them until mid-winter. He did have on a clean shirt and neatly mended overalls.

The Cunninghams don't have much and Walter can't even afford shoes, but he has a clean shirt and neat overalls in an effort to present himself well.

Walter also treats his teacher with respect. When she presses him about forgetting a lunch that he can't afford to bring, he simply agrees with her. When she offers him a quarter that he can't repay, he refuses to take it. His language is respectful and his actions are gracious.

Burris Ewell, on the other hand, takes no sense of pride in himself, which is notable in his appearance:

He was the filthiest human I had ever seen. His neck was dark gray, the backs of his hands were rusty, and his fingernails were black deep into the quick. He peered at Miss Caroline from a fist-sized clean space on his face.

Equally poor, the boys differ in outer appearance. And when Burris opens his mouth, he is downright nasty to their teacher. He snorts at her with contempt and laughs about circumventing the truancy laws. When Miss Caroline asks him to leave, his reaction is insolent:

Report and be damned to ye! Ain’t no snot-nosed slut of a schoolteacher ever born c’n make me do nothin‘! You ain’t makin’ me go nowhere, missus.

The boys are different because the Cunninghams have influenced Walter to be kind, respectful, and gracious. The Ewell family is guided by a drunken father who beats his children, and his nasty attitude has influenced young Burris. The message in their differences is that a child's greatest predictor of success or failure is not his economic status—it is his family's influence in shaping his core values.

At one point in the novel, Atticus explains to Scout that the term "nigger-lover" is used by "ignorant, trashy people . . . when they want a common, ugly term to label somebody." This judgmental language is unusual for Atticus, but it communicates a message from Harper Lee, one that is echoed in her characterizations of Walter Cunningham and Burris Ewell.

Both of these boys may come from poor families, but Walter has been raised with some understanding of respect, while Burris has not. Burris is the type of person Atticus describes as "ignorant" and "trashy," as he is a child version of his father, Bob Ewell, whose cruelty and ignorance is apparent throughout the story. Burris is rude to his teacher, and disrespectful in general, reflecting the absence of proper parenting. Walter, on the other hand, has been taught well by his family, and his manners and respectfulness reflect the stronger values of the Cunninghams.

Harper Lee's message to the reader is one that emphasizes the importance of education. Ignorance, as Atticus explains, can be horribly ugly, and Burris's ignorance contrasts with Walter's ethical awareness. This separates the two boys, despite their shared poverty.

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. 

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.

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.