"Politically incorrect kindergarden" joke

It's getting close to going home time at the infants school. Teacher is chatting to the kids.
Teacher: Johnny, what did you do today?
Johnny: I played in the sand pit, miss.
Teacher: That's very good. I'll let you go a bit early, if you can spell' pit'.
Johnny: P-I-T, miss.
Teacher: Very good, off you go. Mary, what did you do today?
Mary: I played in the sand with Johnny, miss.
Teacher: I'll let you go if you can spell' sand'.
Mary: S-A-N-D, miss.
Teacher: Well done, off you go. What about you Leroy?
Leroy: Johnny and Mary wouldn't let me play in the sand pit, miss. I think it's blatent racial discrimination.
Teacher: Well, if you can spell' racial discrimination...'