In Harper Lee's To Kill a Mockingbird, Scout actually has two ages that have different affects on the tone. Scout the narrator is actually an adult reflecting on things that happened during her childhood. As an adult, Scout the narrator captures a very serious, reflective tone as she develops serious themes concerning morality and racial prejudice. On the other hand, Scout the character is a young child, beginning at the age of 6 and ending at 9. As an innocent child with an excellent sense of humor, Scout the character adds humor and playfulness to the tone.
The seriousness of the tone is reflected in multiple scenes within the book, especially in any scene dealing with racial tensions. For example, in Chapter 15 Scout, the adult narrator, makes some observations that underscore the seriousness of the mob scene, a seriousness that escaped the young child Scout. Specifically, the adult narrator describes Maycomb's jail as the "most venerable and hideous of the county's buildings." She continues to describe it as something that an insane person would have thought up, a "miniature Gothic joke." The hideousness of the building in conjunction with the narrator's reference to Gothicism helps underscore the narrator's serious tone as she depicts an equally hideous, dramatic moment in the story, a moment in which a lynch mob appeared at the county jail to attempt to take justice, as they see it, into their own hands.
In contrast, Scout the child character frequently creates a humorous tone through her witty remarks and antics. Scout makes plenty of witty comments all throughout. One example is seen when, after she asks permission to visit Calpurnia in her home, Scout's father and Aunt Alexandra get into a quarrel. Eavesdropping, Scout thinks they are quarreling about her when she hears her aunt say, "...you've got to do something about her ... You've let things go on too long" (Ch. 14). Fretting that her aunt is proposing Scout should be forced to act more like a girl, Scout thinks to herself the following humorous response:
Who was the "her" they were talking about? My heart sank: me. I felt the starched walls of a pink cotton penitentiary closing in on me, and for the second time in my life I thought of running away. Immediately. (Ch. 14)
Humor is seen in the fact that Scout equates acting like a girl to being forced into a pink prison. The humor of Scout's comment helps create a humorous tone despite the fact that the scene is again about racial tensions.
Author Harper Lee uses both a serious and humorous tone to speak of weighty subjects in the story in order to speak of social injustices with compassion. Like Atticus, Lee sees that people have a tendency to act atrociously due to racism, but also like Atticus, Lee sees that human beings are generally good people who can be viewed through compassionate eyes despite any misdeeds.