Walter wouldn't explain why he wouldn't take money from Miss Caroline, so Scout stood up for him. In doing so, she got punished and was somewhat justified in hurting Walter.
"Catching Walter Cunningham in the schoolyard gave me some pleasure, but when I was rubbing his nose in the dirt Jem came by and told me to stop." Page 22
Jem barely knew who Walter was, he only knew that his sister was mad at him, and he invited Walter over anyway.
"Jem suddenly grinned at him. 'Come on home to dinner with us, Walter,' he said. 'We'd be glad to have you.'" Page 23
A theme of grace is represented by this scene because Jem stops his sister from assaulting Walter without knowing why she is attacking him. Then, he invites Walter, a kid who he doesn't know and his sister despises, over to eat dinner with his family.
"'Hush your mouth! Don't matter who they are, anybody sets foot in this house's yo' company, and don't let me catch you remarkin' on their ways like you so high and mighty!'" Page 24.
"It was not often that she made crackling bread, she said she never had time, but with both of us at school today been an easy one for her. She knew I loved crackling bread." Page 29.
Calpurnia reprimands Scout for complaining about Walter's way of eating. Calpurnia had every right and reason to do what she did, but when Scout came back home Calpurnia fed Scout crackling bread and was nice to her, despite Scout's attitude, demonstrating the theme of grace again.