What factors contribute to Scout's character traits in Harper Lee's To Kill a Mockingbird?

Jean Louise “Scout” Finch has proved an enduring character in American fiction in part because she is very much her own person. While some of her behavior stems from her personality, the way she expresses herself and the changes she undergoes have a lot to do with her unusual circumstances. Especially in growing up without a mother, both she and her brother, Jem, are often left to fend for themselves.
Scout is a smart person with a well-developed vocabulary, which she is proud to use (sometimes incorrectly). Generally a perceptive person, Scout has many blind spots. Although she knows on some level that her family is well-to-do in comparison to other townspeople, she tends to naturalize their situation and to treat less fortunate people as idiosyncrasies: she is a bit of a snob. This flaw is tempered, however, by the fact that she learns quickly; the reader does not see her repeating mistakes, and Lee often shows her being genuinely kind.
Scout also shows a remarkable ability to think on her feet. Although she is dominated by her brother and, to some extent, marginalized by his growing friendship with Dill, she is often the one who thinks up ways to deal with difficult situations. Nowhere is this more evident than in the memorable scene where she uses her gift of gab and her outgoing personality to derail the volatile situation at the jail. By appealing to Mr. Cunningham’s humanity and perplexing the other men by sounding like a miniature attorney, she wakes them up to the unacceptability of their contemplate course of violence and effectively saves at least one life.

Scout's character traits are a product of nature and nurture. Like most people, her character is a synthesis of both. She's naturally a free-spirited young lady, a tomboy who feels much more comfortable in a pair of dirty old overalls than in a dress. Scout has grown up in a male-dominated environment, and despite Aunt Alexandra's best efforts at turning her into a fine, upstanding Southern lady, she identifies more closely with the traditional male role.
As with her brother, Scout's character has been molded to a considerable extent by Atticus. As she gets older and starts finding out more about the world around her, Scout's developing worldview becomes shaped by Atticus's values: his integrity, his endless capacity for empathy, his passionate belief in justice, and always doing the right thing. Scout is very much her father's daughter, yet still retains her strong sense of individuality, and Atticus wouldn't want it any other way.