Gary Paulsen is one of those rare writers whose children and teen books are so well-written that adults can enjoy them.
This whole series works as a great coming-of-age story, as historical (western) fiction, and as an adventure. My son was about 4th grade -5th grade when we read the whole series together. It is often rough and gritty and portrays some of the less attractive sides of human nature. It is also exciting, character-driven, and very vividly descriptive. As both a reader and a mom I recommend it.
Fourteen-year-old Francis Tucket is heading west on the Oregon Trail with his family by wagon train. When he receives a rifle for his birthday, he is thrilled that he is being treated like an adult. But Francis lags behind to practice shooting and is captured by Pawnees.