The Cunninghams and the Ewells comprise the two poorest families in Maycomb County. Walter Cunningham demonstrates his family's values by refusing to accept charity when it is offered by their teacher. The Cunningham's attitude is such that they are "poor but proud," meaning that they may have little money, but they refuse to prevail upon others for assistance.
This trait is unlike the Ewells, in that the Ewells are poor and ignorant. Land owners allow the Ewells to poach because they know the family's shabby state, and they are also excused from most of the school year due to their background.
Walter Cunningham is from a very poor family in Maycomb. They are poor but they are also very proud member. He won't take a handout because his family may be poor, but they do not take charity. They believe in getting what you need but not asking for any help. The teacher doesn't really understand the values of the social structure in Maycomb and when Scout tries to tell her that Walter won't take charity, she gets into trouble.