You see, Sir - you're going to give me good marks.
And good approval. And let me do what I want.

Because I know about you, Sir - and your fetishes - and, well, it'd be a shame if they got out - wouldn't it, Sir?
So, you see Sir... well... you help me and, well, I keep this a secret.

The school bully blackmails the headmaster - keeps them out of trouble and ensuring the good marks are granted.