Cassie's relationship with Lillian Jean symbolizes the racist and prejudicial situation that exists in the South. The conflicts between the two young girls serve to show the effects of a racist society. Racism and prejudice is learned. Lillian Jean is just twelve years old, and she has already been taught to treat Cassie with disrespect and hatefulness.
Cassie is only nine, but she has been taught by her parents to have pride, determination, and courage. Yes, she does plot revenge against Lillian Jean, but it is because she refuses to accept the treatment of blacks as an acceptable fact of life. Her type of revenge reflects her young age, but her determination to make things better never diminishes. She isn't afraid to speak up when she sees the unfair treatment of her grandmother and herself when the store owner waits on white customers first. She knows it's wrong to get the hand-me-down books of the white school children.
So, what's the message? I think it's a message of hope that Cassie represents those who eventually do stand up against prejudice and unfair treatment. Cassie is the future because she challenges the white power structure. Cassie's independence symbolizes how important freedom from the existing sharecropper system is for her family. The Logan family's independent spirit is symbolized in Cassie in the hope that her generation will make it better.