LOSS OF INNOCENCE. Jem and Scout are the human mockingbirds of the story, experiencing many tribulations that children their age should never encounter. They are forced to deal with others' taunts about Atticus; they deduce the lies that are told to them by adults; and they become the innocent victims of a murderous attack by Bob Ewell.
PREJUDICE. Atticus teaches his children to "climb into his skin and walk around in it" before judging people. Racism is rampant in Maycomb: The Ewells are the most obvious example, but it is obvious in many characters, including Miss Stephanie, Mrs. Merriweather, Aunt Alexandra, Miss Gates and the Cunninghams. Mr. Avery displays prejudice against children, and most of the town believes that Boo is responsible for "Any stealthy small crimes committed in Maycomb" simply because of his rumored mental instability.
COURAGE/COWARDICE. Atticus and Mrs. Dubose show courage in different ways than the typical "idea that courage is a man with a gun in his hand." The least likely character to display heroism is Boo Radley, who risks his own life to protect Jem and Scout. Bob Ewell is the epitome of a coward, as is Scout's cousin Francis, who taunts Scout and then runs and hides behind Aunt Alexandra's skirt.
KNOWLEDGE/IGNORANCE. Teachers, the supposed purveyors of knowledge, are shown to be among the most ignorant people in town. Many of the people of Maycomb fear Boo Radley and Dolphus Raymond because of their own ignorance and fear of the unknown, while the Ewell family remains ignorant for their simple refusal to take advantage of free public education.