I think we've addressed this topic before.
Reffing High School is a tough gig. The extremely wide variation of the age groups and skill levels of the players on the pitch makes calling a game difficult.
Some of the players are highly skilled, while others are very weak. A ref has to quickly learn who is who on the field. A skilled player will usually prefer to play through the frequent minor fouls committed by unskilled players, while fouls intentionally committed by skilled players against unskilled kids simply can't be tolerated at all.
A good ref will know what to call and what not to call. But if done with perfection, it will appear as if he is not calling the game fairly. Screams of "CALL IT BOTH WAYS" will certainly be heard coming from the coaches and benches, while meanwhile the ref is perfectly only calling the things that the players at each particular match up want called.
In many other cases, the refs simply suck.