In Chapter 21 of To Kill a Mockingbird, why are Calpurnia and Aunt Alexandra upset?

In chapter 21 of Harper Lee’s To Kill a Mockingbird Calpurnia and Aunt Alexandra both become upset when they learn that Jem and Scout have been watching the trial of Tom Robinson. They believe that the content of a rape trial is not appropriate for such young children to hear.

When Calpurnia scolds the children for being in the courthouse, we see some character development for Jem. Up until now, Jem, along with Scout, has been pretty well contained under Calpurnia’s thumb. Now, however, Jem has gotten a little older and a little wiser, and is beginning to think more for himself. Look at how he reacts to Calpurnia’s words:

“When you oughta be hangin;’ your head in shame you go along laughin’—“ Calpurnia revived a series of rusty threats that moved Jem to little remorse, and she sailed up the front steps with her classic, “If Mr. Finch don’t wear you out, I will—get in that house, sir!” Jem went in grinning . . .

Notice that Calpurnia’s attempts to discipline Jem are now having little effect. When he should be worried or cowed he is grinning. This demonstrates that Jem is maturing and forming his own ideas of right and wrong that are not necessarily subject to the admonitions of someone besides Atticus.