Scout learns a lot about human nature before the trial even begins. She learns about racism and prejudice, and about the inequities blacks and whites face in Maycomb.
First of all, Scout learns about racism and prejudice when people begin teasing her because her father is defending a black man. She does not understand why this is such a big deal.
“…He made it sound like you were runnin' a still."
Atticus sighed. "I'm simply defending a Negro- his name's Tom Robinson. (ch 9, p. 53)
Atticus is concerned with Scout’s temper. He is worried that she is going to lose her head because people will keep teasing her. He knows that his children will be relentlessly attacked not just by adults but by kids.
Scout gets a lesson in inequity when she goes to church with Calpurnia. She is not accepted with open arms by everyone there. She also learns that most blacks cannot read.
During the trial, Scout learns to sympathize for Mayella Ewell, even though she is on the opposite side.
As Tom Robinson gave his testimony, it came to me that Mayella Ewell must have been the loneliest person in the world. (ch 19, p. 136)
Finally, the trial itself is a good example of inequality. Scout is old enough and smart enough to realize that Tom Robinson could not physically have committed the crime. Jem is actually more upset when Robinson is convicted than Scout is, because he seemed convinced that the jury would acquit.