In our area we send the newer guys to work lower level ball but we send an experienced partner, who is usually on the bases. That way we can observe the strike zone and mechanics of the new guy. At the end of the HS season this year, we had a middle school game that had two very experienced umpires on. The BU is a pro school graduate, a D1 umpire that has worked a conference tournament the last three years, and is the field mechanics instructor for our group. I was the PU, also a D1 ump and the local rules interpreter. We had more **** from the coaches than any varsity game either of us worked all year. At the end of the game the home manager was convinced the BU was horrible and didn't have a clue. I assure you that he never missed a call and never missed a rule but if you asked the manager the story would be completely different.
I managed a Pony team this year and I had a kid who was convinced 5 PUs in a row had a terrible strike zones. I told him to shut up and swing the bat. Also, I told him if he wasn't hitting 700 to never argue ball and strikes.