What's something that a member of the high school faculty could really do to cheat a student?

Someone on another board I visit had a teen-age son who wrote an entry for an essay contest about something that happened after he delivered a stand-up speech. Tom (that's the boy's name) did a comedy routine in the form of a speech at a school event. Before the event, the principal read over his paper and he approved all the jokes he put in there. In this speech, Tom said that the students who went to a "bad" college could do this or they could do that . . . or they could just end up becoming teachers at his school. The principal changed his mind and complained that he didn't like that comedic stab at the quality of his high school's teachers. He lied and said that he had told Tom he couldn't read that part. Tom said the principal was lying when the principal complained to another authority figure, and the authority figure believed the liar. Tom was banned from doing any more stand-up. The ban was ended, however, when this essay got published and the second authority figure here realized Tom was telling the truth after all.

Then there are the teachers who deliberately lose their students' tests, and who fail the students whom they don't like.

Has anybody got a good idea for something I could have the assistant-principal do?