"Little Johnny at Spelling Competition" joke

Teacher: We are going to have a spelling competition this afternoon. Anyone who can spell a word
correctly can go home early. We'll start with Mary. What did you do at lunchtime?
Mary: I played in the sand-pit.
Teacher: Mary, can you spell "pit?"
Mary: P... I... T?
Teacher: Very good, you may go. Now Tommy, what did you you do at lunch?
Tommy: I was playing with my toy car.
Teacher: Tommy, can you spell "car?"
Tommy: C... A... R.
Teacher: Very good, you may go. Now Johnny, why are you crying?
Johnny: (sniff)' Cause Tommy and Mary wouldn't play with me at lunchtime, just' cause I'm black
(sniff).
Teacher: My my. That's racial prejudice. Johnny, can you spell "racial prejudice?"