Miss Caroline Fisher is a new teacher and, more significantly, a newcomer to Maycomb. She is from Winston County in northern Alabama, which might as well be the moon, at least from Scout's point of view. Miss Fisher's lack of insight into Maycomb affords Lee the opportunity, through Scout, to communicate to both Miss Fisher and the reader some of the social dynamics of this small town.
For example, when Walter Cunningham comes to school without a lunch, Miss Fisher tries to lend him a quarter. However, Walter won't take it. Miss Fisher doesn't understand, and it is left to Scout to explain the situation. She tries to tell her that although very poor, the Cunninghams are proud and will never accept money they can't pay back. Since Walter knows he can't repay the quarter, he would rather go without lunch. We begin to understand that poverty is an everyday aspect of life in Maycomb and that pride is an important and accepted social trait.
Further, the students laugh when Miss Fisher hits Scout's hand with a ruler, seeing this as impossibly wimpy. They are used to real whippings. We thus learn that Maycomb is a rough and tumble, old-fashioned place, one not filled with fragile people.