To the above answer I would add that Scout is unusually smart and insightful for a child of her age. However, her strong-willed nature and her innocence often get her into trouble with her family and with society as a whole. As a narrator, we must scrutinize the details that Scout provides us. Sometimes, she tells us those details completely and accurately; sometimes she herself does not fully understand what exactly has transpired. Although she does indeed seem more comfortable among adults rather than children her own age, she isn’t always capable of fully comprehending that adult world. As readers we must learn to “read between the lines” of what Scout relays to us and infer the details she sometimes leaves out.
The word that my students always use for Scout is "Tomboy". She plays outside, dresses like a boy, and beats up other boys.
Additionally, she is intelligent, insightful, and imaginative. She learned to read at a young age, innocently questions extremely difficult societal questions, and she plays creative games, such as the Radley reenactments, with Dill and Jem.
She lacks a “proper” feminine influence, in her life and really has no interest in learning how to act like a lady. Aunt Alexendra attempts to make Scout act like a lady by forcing her to attend Maycomb’s ladies missionary circle and dressing her up in a dress. Scout detests Alexandra’s attempts at making her a lady.
Scout is an unusual little girl for the time when the book is told. She is brought up to speak her mind. In her home both children are treated as equals, there are no boy or girl activities. The first time she is treated as a "girl" is when she is made to wear a dress and shoes to school. Atticus has taught both Jem and Scout how to read and write and both children do well at these skills. She also is willing to speak her mind and had no fear doing so to any adult. She is unusual, because she does not recognize ratial or age boundaries. She is more comfortable with adults than with children. For today's standards she would fit in perfectly, but in the 50's she is considered as outspoken and even disrespectful. Children were meant to be seen, not heard.
She is smart and a tomboy and she already knows how to read at such a young age. She is not entirely feminine and her aunt wants her to conform to the roles held for women in society wearing feminine clothes. Scout can stand up for herself and others and as she matures her understands with other people also improves.