I slapped my nephew
What? Why did you slap your nephew?
He is doing poorly in school.
You are being a child abuser by slapping your nephew. You should never put your hands on another person. You should get your nephew a tutor so that he can improve his studying skills and bring his grades up.
I don't have time to take him to a tutor. This is what he gets for being a loser.
It's never okay to hit a child. It also is extremely unlikely to have any positive impact on his efforts at school. Maybe his school has tutors available so you wouldn't need to spend time on it.