A thesis statement should be as specific as possible, but should be written without fully arguing the points you plan to discuss. You should hint at where your argument will go, so your reader gets an idea of the paper and can follow the development of your argument. A thesis statement that says characters go through experiences is not specific enough to help the reader understand where the essay will move.
Think about the events of the book that teach Scout something about her community. Reviewing the events can help uncover a thesis statement that is more specific to the book. One can argue that Scout learns to have empathy and compassion through her struggle to understand the townspeople's racist and judgmental attitudes. For instance, people immediately assume that Tom is guilty because he is black. While the people intensely dislike the Ewell family, they still take their side because they are a white family. The children discover this underlying prejudice in society only after seeing their neighbors try to lynch Tom without a trial, seeing their friends turn against their family for helping Tom, and witnessing Tom's incarceration even though Atticus clearly proves Tom's innocence.
It is only after these terrible events that the children discover that their world is not perfect. Even the people they respect can have faults. Scout takes what she learns and applies it to her dealings with Arthur (Boo) Radley. She learns to have compassion for his plight and not judge him unfairly when she does not really know him.
The argument here is that only by living through unfortunate times do people learn the truth about others and about themselves. Only then are they able to grow as individuals and apply what they learn to other situations.