In Jem's ranking of social classes in Maycomb, he separates them into four groups: regular people (like the Finches and their neighbors); poor people like the Cunninghams in Old Sarum; the Ewells (they stand alone); and Negroes. The Cunninghams are mostly poor farmers who have been hit hard by the Depression. They are basically honest (the penniless Walter Sr. repays Atticus for his legal services with farm goods even though it takes him months) families who live a rural lifestyle different from those in Maycomb. The Cunninghams were

... an enormous and confusing tribe domiciled in the northern part of the county... They did little, but enough to be discussed by the town and publicly warned by three pulpits: they hung around the barbershop; they rode the bus to Abbottsville on Sundays and went to the picture show; they attended dances at the county's riverside gambling hell, the Dewdrop Inn & Fishing Camp; they experimented with stumphole whiskey.  (Chapter 1)

Walter Cunningham Jr. came to school undered, with worms and with no lunch money, but he wore clean clothes and he was polite. Walter Sr. came to the jail with the intention of lynching Tom Robinson, but his conscience would not allow him to commit murder after being shamed by Scout's innocent conversation. One of the Cunninghams sat on the jury--and may have been part of the lynch party--but he was the last member to be convinced to vote Tom guilty.

The Ewells, on the other hand, had

... been the disgrace of Maycomb for three generations.  (Chapter 3)

One can only wonder how Bob's father and grandfather could have been more scurrilous than their offspring. Bob drank up his welfare check, providing little for the rest of the family. His son, Burris, appears at school one day a year--filthy, lice-ridden, and full of insulting curses aimed at his female teacher. Bob apparently beat his own daughter, concocted the story of rape because of his hatred for Negroes, and ultimately caused the imprisonment and death of Tom Robinson. But that was not enough. He still wanted revenge against Atticus, who had made him look foolish on the witness stand; and Judge Taylor, who was not fooled by Bob's lies. Unlike the Cunninghams, who only considered murdering Tom--who they believed guilty of raping a white woman--Bob was bent on killing Jem and Scout--innocent children--to enact his revenge on Atticus. 

Scout liked Walter and wanted to be his friend. Her Aunt Alexandra didn't recognize the difference between Walter and Burris Ewell.

"Because--he--is--trash, that's why you can't play with him..."  (Chapter 23)

But Scout did.

"... Walter. That boy's not trash, Jem. He ain't like the Ewells."  (Chapter 23)