When is Cassie seen as mature?

Cassie's difficult path toward adulthood passes another milestone when she realizes the implications of the cliche that life is not fair. Approaching Mr. Barnett to remind him that they have been waiting, Cassie expects that he will react as she does and perceive the unfairness of her situation. When he does not, Cassie is doubly outraged, both by the injustice of his racist reaction and by this upset of her generally positive worldview. Cassie begins to see the reality of being black in a world dominated by whites.