Scout comments that there is not much else left for her and Jem to learn "except possibly algebra" in Chapter 31, right as the novel is coming to a conclusion. This naive (but sweet) comment references just how many adventures the siblings have had over the course of the book, many of which served as significant learning opportunities that taught them the ways of the world: the blatant racism of the South, the nature of personal sacrifice and friendship, the power of courage, the role that judgment plays in society, etc. Scout, in particular, has experienced a great deal of personal growth; she has evolved from being a rather clueless little first grader with an angry streak to a much more even-tempered, tolerant girl. Although she still has a long way to go in the arc of her growing up, Scout has matured significantly. After the many struggles of the past two to three years, from watching Tom Robinson be wrongfully accused of rape to being attacked by the crazed Bob Ewell, the fact that algebra may be her only challenge is a true blessing.
This quote can be found in the final pages (Chapter 31) of To Kill a Mockingbird. Scout has seemingly experienced all that life has to offer: She has discovered that the rumors about Boo Radley are not true, and that he is actually her protector, coming to her rescue when Bob Ewell attacks the children. Her fantasy is fulfilled: She sits with Boo on the porch swing just as she had dreamed. She has witnessed the cruelty of men and how some people (particularly, the jurors) abuse their power. She has witnessed how the innocent are punished for crimes they did not commit (Tom Robinson and Boo). She learns about the various types of courage displayed by both men and women. She has learned about love (Dill), and important lessons concerning intolerance taught to her by Atticus. For her,
... there wasn't much else for us to learn, except possibly algebra.