In Chapter 3, Walter Cunningham Jr. is eating with the Finches. Scout makes fun of the way Walter eats and Cal scolds her for doing so. Cal tells her:
Don’t matter who they are, anybody sets foot in this house’s yo‘ comp’ny, and don’t you let me catch you remarkin’ on their ways like you was so high and mighty! Yo‘ folks might be better’n the Cunninghams but it don’t count for nothin’ the way you’re disgracin‘ ’em—if you can’t act fit to eat at the table you can just set here and eat in the kitchen!
By 'better than' ("better'n"), Cal means that even though the Finches are more educated and have more money, that doesn't mean they (or anyone) has the right to mock those of a lower social class. Scout probably doesn't grasp the notions of class here, but she does learn a lesson to be respectful to others, regardless of who they are or where they come from.
In Chapter 12, Scout discovers that Cal lives two separate lives: her life with the Finches and Cal's life with her own family and African-American community. Here, Scout gets an introduction into the way the two races are segregated in Maycomb:
That Calpurnia led a modest double life never dawned on me. The idea that she had a separate existence outside our household was a novel one, to say nothing of her having command of two languages.
This trip to Cal's church clues both children in to Cal's other life. Jem learns that most of her congregation can not read. Cal tells them that she learned to read from the Bible and an English law book. It had probably never dawned on Jem (or Scout) just how limited the opportunities were for African-Americans, even for Cal.
“Why yes sir, Mister Jem.” Calpurnia timidly put her fingers to her mouth. “They were the only books I had. Your grandaddy said Mr. Blackstone wrote fine English—”