My '05 son was pitching in a tournament game this weekend. By the middle of the game he had the Catcher set his target in the middle of the plate because he found he couldn't get any calls on the corners. The other team had some good hitters at the top of the order, but some kids who realistically were overmatched at the bottom.
After the game the umpire came up to him and said "I'm sorry, but I had to do something" and went on to explain that he narrowed the strike zone because my son was dominating the hitters too easily.
It worked out OK as he pitched a 2 hit complete game shutout, but he probably could have saved 20 pitches or so on his arm. I think he needs to be working on hitting his spots, not throwing the ball down the middle. I think by the time kids are HS age, the umps would just call it straight and let the results fall where they may.