How does Scout get in trouble at dinner in To Kill a Mockingbird?

You are probably referring to the scolding that Scout
receives from Calpurnia in Chapter Three. On the first day of school (Chapter Two),
Scout gets off "on the wrong foot" with her new teacher, Miss Caroline. She blames
Walter Cunningham Jr., so she rubs his nose in the dirt at the beginning of lunch hour.
Jem breaks it up and invites Walter back to the Finch home for a home-cooked meal.
Atticus is happy to see young Walter and treats him like a welcome guest. But Scout,
still angry at him, makes fun of him for pouring syrup over all of his food. Calpurnia
escorts Scout from the kitchen and gives her a good lecture. Afterward, Scout demands
that Atticus fire Calpurnia, but he refuses.