Mrs. Caroline doesn't understand that Scout is a advanced learner due to her father Atticus. From where she learned from she assumes all children her age are, in a nicely way put "dumb". Along with not knowing the county's traditions as she is a outsider, when all the students aren't the way she thought they would appear to be because again, this is her first job and she prepared everything around how she thought'd they be. When Scout proves more intelligent than the rest, Mrs. Caroline doesn't know what to do. Not only are the rest of the students not what she expected and "dumber" or not paying attention, she has one student who is way ahead in learning. The teacher is frustrated and takes her frustration on Scout as she slaps her hand and tells her to stop learning. Again only doing this because she has students who are not what she expected, and it exhausts her.
Hope this helped~
- Kathryn Irene