In Harper Lee's To Kill a Mockingbird, why is Scout so anxious to begin school?

Like so many young children who have watched their older siblings and friends go off to school each day, Scout wants to be included.  She is used to the companionship of other children, and when the older ones are in school she is left alone to play by herself each day.  She recalls sitting alone in a treehouse overlooking the schoolyard, "spying on multitudes of children...learning their games, following Jem's red jacket through wriggling circles of blind man's buff, secretly sharing their misfortunes and minor victories...I longed to join them" (Chapter 2).  She doesn't really have a concept of what school entails other than the fact that the students, who seem to be having fun on the playground, go there everyday and she is not allowed to be with them.