Scout gets in trouble because she knows how to read (the teacher cites she's been taught incorrectly), for explaining why Walter Cunningham won't take a twenty-five cent loan for lunch money, and then finally saying straight out that Walter can't afford to pay her back (Scout is slapped with a ruler). Lastly, the children end up bringing Walter home for lunch where Scout is chastised for being rude to a guest. It was a rough day!
Hope this helps!