Dill had left Maycomb at the end of the summer to return to his home in Meridian, and Scout was "miserable" until she remembered that her first day of school was just around the corner.
I never looked forward more to anything in my life.
She had spent much of her previous winter in the treehouse, spying on the children in the schoolyard with her telescope, where she watched Jem playing games in his red jacket,
... secretly sharing their misfortunes and minor victories. I longed to join them.
Atticus apparently paid Jem to walk her to school on the first day, since Scout heard "an unfamiliar jingle" in his pockets. Jem then laid down the law, telling her that they could not be seen together during school hours.
I was to stick with the first grade and he would stick with the fifth. In short, I was to leave him alone.
Jem told her that things were different at school, something that Scout would soon see for herself when she met her new teacher, Miss Caroline.