Scout is unusal for a first grader because:

Scout is far ahead of all the other first graders in her
class because her father, Atticus, taught her to read several years before. Scout
couldn't remember not knowing how to read, especially the hymns sung "in the long hours
of church." She had also been "wallowing illicitly in the daily papers." She and Atticus
read together every night, so it had come second nature to her. Additionally, Calpurnia
had taught Scout to write in cursive (which many students don't learn till third grade),
so Scout truly was way ahead of the rest of Miss Caroline's first graders. Scholastic
skills aside, Scout is also pretty tough and has no qualms about picking (and winning)
fights with the boys in her class.