Why does Harper Lee include the information on Mr. Cunningham's dealings with Atticus, in the middle of the classroom scene?

Lee uses the information about Mr. Cunningham's dealings with Atticus to support Scout's statement that "The Cunninghams never took anything they can't pay back." The information reveals a little about the Cunningham's poverty but also how they are respected. This is important for the reader to distinguish between the Cunningham family, who are making good choices and earning people's respect, and the Ewell family, who are similarly poor but do not have the respect of the townspeople.