Atticus discusses mobs with Jem and Scout in a way that causes them to see a group such as that in a way that is much different that it might first appear.
"...A mob's always made up of people, no matter what. Mr. Cunningham was part of a mob last night, but he was still a man. Every mob in every little Southern town is always made up of people you know--doesn't say much for them, does it?"
"I'll say not," said Jem.
"So it took an eight-year-old child to bring "em to their senses, didn't it?" said Atticus. "That proves something--that a gang of wild animals can be stopped, simply because they're still human. Hmp, maybe we need a police force of children...you children last night made Walter Cunningham stand in my shoes for a minute. That was enough."
In teaching his children to view people as individuals, rather than groups, Atticus taught his children a valuable life lesson. He also taught them how powerful even a child can be. By showing them these aspects of a mob, Atticus taught Jem and Scout that they did not need to fear it.