In "To Kill a Mockingbird", what is the effect of Calpurnia on Scout, and why is this effect important?

Because Scout has no mother, and she runs "wild," as stated by Mrs. Dubose, Cal creates a sense of rules and regulations. It is not odd that during this time in the South the "help" would teach manners to the young and teach the basic principles of their culture (even if they were from different races). Many families allowed the nanny to raise children--and most were African-American nannies, or "mammies."

Calpurnia can scold and even spank Scout, which is something that Atticus rarely does. He explains the world, but he doesn't really have time for child rearing.