Scout certainly had a big letdown after attending her first day of school in To Kill a Mockingbird. Although Miss Caroline is fresh out of college, she seems to have few social skills when dealing with her students. Scout stood up for Walter Cunningham Jr. when Miss Caroline unintentionally offends him. The students didn't understand the "imaginative literature" of Mrs. Cat and the drugstore, and Miss Caroline didn't bother to explain it. Miss Caroline made Scout feel as if she had committed a crime by learning to read before the first grade. When punished later by a ruler-spanking of her hands, Scout found Miss Caroline's action more amusing than academic.
Jem does not help matters. He tells Scout to be patient about the new teaching method being initiated by Miss Caroline. "'It's the Dewey Decimal System,'" Jem tell Scout, who "never questioned Jem's pronouncements." However, Jem was also confused: Miss Caroline's new teaching style was based on the educational reformer John Dewey (1859-1952)--not the library system of organizing founded by Melvil Dewey.
You can find this in Chapter 2.
Scout hates current fashions in education. At least she hates the fashion in education that is brought to her school by Miss Caroline, her first grade teacher. Scout gets bored by what is going on in class and starts writing a letter to Dill.
Miss Caroline wants the kids to sit there while she reads them long and boring stories. She wants them to just look at flash cards that she shows them. She gets angry when she finds out that Scout already knows how to read. She says that Scout has been damaged by that.
So Scout is pretty unhappy about this particular (Dewey Decimal System) educational fashion.