A hallmark of an experienced performer is knowing when a problem is not about you.
Someone else has a cold, or the sound isn’t working right, or your collaborator is going through a divorce, or even the weather: I’ve seen all of these situations lead to shaky rehearsals or performances.
My experience is that most high school students – even many with a wealth of experience – think that any shaky moments are somehow caused by them. I know I thought that many times when I was growing as a musician.
It’s important, if given the opportunity, to give student context to know when something is in their control and when it really isn’t. When an ensemble is suddenly not tuning well, there is probably some reason. A tenor getting mad at the basses for singing flat isn’t likely going to fix that problem if it’s not about them. (Maybe your lead bass has an undiagnosed ear infection…don’t get mad without considering context!)
Don’t let your students fall down the rabbit hole of feeling like a failure when bad days happen. Often, they’re not about you.
Remind them to keep doing their best, trust the process, and trust each other. The rest will solve itself in time.