Scout, the lawyer's daughter, wants to keep things fair, so she goes to the trouble to explain to the new teacher Miss Caroline why Walter Cunningham can't or won't accept a quarter for lunch. This backfires, as Scout has already offended the teacher with her reading skills learned at home. Miss Caroline isn't at all disposed to learning anything else from Scout Finch since, after all, she is the teacher and Scout the student.
Walter Cunningham represents the working poor, who despite their poverty want to keep their dignity and honour. As his father who pays Atticus Finch back little by little through entailment in whatever way he can, it's important to Walter to not get into a debt he cannot get out of, even if he has to do without lunch.
Burris Ewell, the saddest case, is infested with lice and is often out of school so that he can stay at home and help out on his father's farm. In fact, he just shows up on the first day for the record so that the truancy officer won't come after him. His family are the down and out poor who are one of the welfare cases of Maycomb, living down by the town dump and eeking out an existence as best as they can. Except for Mayella, the Ewells have no pride or motivation to strive for a better life. Burris with his "cooties" is indeed the spitting image of his father.