The Extras is inspired by classic boarding school stories.  These stories are based,  sometimes more accurately, sometimes less, on life in traditional or old fashioned boarding schools.  And in these schools, there are prefects.  Who are the prefects, anyway, and why are they bossing everybody around?
 
Prefects are older students in the top years who are given some responsibility for the running of the school.  This is supposed to be a tribute to their growing maturity, and is designed to give them real leadership experience and help them develop their characters by providing them with challenges and problems to solve.  Prefects may organize student clubs and activities, manage and coach sports teams, and represent student interests in meetings with the faculty, the board, and even sometimes local government.
 
But where we see prefects most often in stories is in their roles as mentors and disciplinarians to younger students.  Prefects supervise the dorms and keep order in study halls and recreation periods.  They are allowed to administer minor punishments on their own, and often slightly larger ones when acting as a group, and of course they will report the most serious infractions to the proper authorities.  But it's not all demerits and extra chores.  Prefects also act as big siblings to their charges, providing them with useful guidance and steadfast support.
 
In a well run school, prefects are carefully chosen for their academic, social and leadership skills, and in turn, good prefects do a lot to make a school better.  But when the wrong people are selected and the prefects' room is full of bullies and sneaks, a school can "go to the dogs" very quickly.