My daughter was playing in a USTA tournament this summer. The ref walked over during a game that she was receiving. She called a serve out that was clearly wide in the center. The ref said it was in and gave the other girl the point. My daughter didn't say anything and ended up winning that game (at which point the ref headed to another court).
On the changeover the other girl said "that serve of mine he called good was wide by 3-inches". The ref seemed like a nice guy and I'm sure thought he made the correct call. Most of them I have seen at USTA junior tournaments are just regular people trying to do the best they can. I do agree with Woodrow that it is usually the parents that get worked up, not the kids.