In Harper Lee's To Kill a Mockingbird, why is Scout nominated as the one to explain Walter Cunningham's situation to Miss Caroline?

In Chapter 2 of Harper Lee's classic novel of the American South and a young girl's coming-of-age in a time of endemic poverty and racism, To Kill a Mockingbird, the story's main protagonist and narrator, Scout, is describing her first day in the first grade. Her young, new teacher, Miss Caroline, has not yet had the opportunity to get to know her students. When she, Miss Caroline, innocently asks to know which students brought...

In Chapter 2 of Harper Lee's classic novel of the American South and a young girl's coming-of-age in a time of endemic poverty and racism, To Kill a Mockingbird, the story's main protagonist and narrator, Scout, is describing her first day in the first grade. Her young, new teacher, Miss Caroline, has not yet had the opportunity to get to know her students. When she, Miss Caroline, innocently asks to know which students brought their lunches, there is one student, Walter Cunningham, who apparently has no lunch box or alternative arrangements for his afternoon meal. The Cunningham family, Scout, through her father, Atticus, will explain, is among the town's poorest, and Walter is regularly without food for lunch. When Miss Caroline, again innocently and with the best of intentions, offers Walter a quarter to buy himself some food, the young boy declines, leading to the teacher's continued confusion regarding her student's circumstances. It is then that Scout intervenes on Walter's behalf in an attempt at diplomatically enlighten Miss Caroline. The reason that Scout, rather than any of the other students in the classroom, speaks up is explained in the following passage from this chapter:

"I turned around and saw most of the town people and the entire bus delegation looking at me. Miss Caroline and I had conferred twice already, and they were looking at me in the innocent assurance that familiarity breeds understanding."

Scout, the reader is quickly informed, is an intelligent and curious child, and generally confident of her place in life, although that confidence does not extend to the mysteries of the world around her. She is not shy, and has, the passage suggests, already engaged in multiple exchanges with her teacher. That is why it befalls to her to speak up for Walter and Miss Caroline's benefit--an exercise that only angers this inexperienced teacher.