Prefects are generally considered to be exempt on the traditions about dobbing (except by their closest friends). They act as a bridge between the boys and the staff and they stand up for the rights of boys if they need to. There’s actually… sort of a catechism that the prefects use. I can’t remember the whole thing, but a bit of it is.
“There is the boy. There is the bully. Where are you?”
“Between them.”
“There is the boy. There is the master. Where are you?”
“At the boys side.”
“There is the train. The boy has fallen. Where are you?
“I’m on the tracks.”