Roll of thunder hear my cry

In chapter 5, Cassie doesn't understand why Mr. Barnett was waiting on the white people before waiting on her.  I think she might not understand that since she is black, she will not be treated as well    as white people.  T.J. and Stacey seem to know this, which makes sense because they are older.  It is wrong that Mr. Barnett didn't wait on them, but in this time period it was okay.