What happens?

The Christmas dinner ends and Scout goes with Francis outside to rest and he starts talking to her. Firs he insults Dill about being unwanted and passed from relative to relative and then insults Atticus's parenting and calls him a "nigger lover" again and she hits him. Uncle Jack comes out and hears that scout called Francis a "Whore Lady" while fighting and after already giving her a warning he decides to discipline her without hearing her side of the story. Later on he comes to talk to her and she tells him, "You're real nice, Uncle Jack, an' I reckon I love you even after what you did but you don't understand children much" He doesn't hear both sides and learns about children from Scout.

Why is it significant?

Even though Scout is young she is wise beyond her years and teaches Jack about parenting even though she still childishly fights. She is not prejudicial and racist like everyone else, she has her own opinions and is caring. It shows Atticus's parenting isn't bad even though he is a detached parent. His moral and smarts rub off on Scout. She tells Jack to leave Francis alone because she says that it wouldn't make a difference now.

What does it tell us about -

Scout

She is very hot-headed and will not hesitate to settle something with her fists. When she is treated unfairly she will speak up but she is wise and knows what is right and wrong.

Atticus

Atticus believes in discipline and he says that Scout deserved the smacking she got from Jack. Atticus has taught her moral values. He also lets her know what she has done wrong. He is diplomatic, always hears both sides of an argument which is why Scout expects the same courtesy from Jack.

Jack Finch

He doesn't have children and doesn't understand them, he hears that Scout swore and straight away she is in trouble. He learns something from Scout and immediately feels that he has done wrong by her.