Why does Scout get in trouble at school

First, Miss Caroline reads a saccharine children's story about cats, which leaves the children feeling restless. Scout explains, "Miss Caroline seemed unaware that the ragged, denim-shirted and flour-sack-skirted first graders were immune to imaginative literature." Half of these children had failed first grade the year before. Therefore, when Miss Caroline writes the alphabet on the board and Scout reads it through easily, then reads from her reader and from the local paper, Miss Caroline forbids Scout to let Atticus teach her to read anymore. Rather than congratulating Scout on her knowledge, Miss Caroline believes Scout is being taught incorrectly and tells her not to read at home anymore.

Later, Miss Caroline asks everyone who isn't going home for lunch to show her their lunch pails. One boy, Walter Cunningham, has no pail and refuses to accept Miss Caroline's loan of a quarter to buy something with. Miss Caroline doesn't understand his refusal, and a classmate asks Scout to help explain. Scout tells Miss Caroline that Walter is a Cunningham, and thinks that explanation should be enough. After realizing Miss Caroline doesn't know what that means, Scout explains that the Cunninghams don't accept other people's help, and just try to get by with what little they have. Scout mentally recollects how Mr. Cunningham, when entailed, repaid Atticus for his legal services by giving the Finch family hickory nuts, stove wood, and other farm produce. The Cunninghams are farmers who don't have actual money now that the Depression is on. Many professionals in the town charge their country clients in farm produce rather than monetary currency. When Scout explains that Walter can't pay back the lunch money Miss Caroline offered, the teacher taps Scout's hand with a ruler and makes her stand in the corner of the room.