Why was Stacey in a bad mood?

Stacy is upset at different times in the book. I'm going to assume that you are referring to Chapter 1.It is early October and the kids are walking to school. Stacy is in a bad mood because he is forced to go to school and forced to wear his Sunday clothes.

Also, Stacy is upset because at school, he is in the class with his mother, which is his school teacher. Cassie makes that clear, because she says, "Shoot, it ain't my fault you gotta be in Mama's class this year."