Why was scout's first day of school a terrible disappointment to her?

Scout could already read and write well and her teacher was not very good; Scout is more experienced than the class already. Atticus tells her to keep going to school, but promises to read with her every night if she keeps it a secret.

You know time is of the essenceyeah i tried lil babyput your feelings to the side lil babyyou got too much pride lil babyi ain't have time yesterdaybut today i got time lil baby

He committed suicide.