I have to yell to get the kids' attention - how do I do that and not ruin my voice?
A client of mine works as a teacher at a place where kids come for field trips and asked how he could speak loudly to get the kids' attention without having to yell and wreck his voice. I thought about how I would position my voice into the higher soprano range which can carry over loud noise. (Think soprano vs. orchestra during an opera.) I practiced a few sounds and checked how it affected my throat and realized it would be very difficult to use that voice position properly on a consistent basis.
What I suggested to my client is that he use a whistle. A whistle makes a high soprano sound that carries over loud noise and doesn't require the use of your voice at all. It does not need to be particularly loud, just high. Tell the students to listen for the whistle so they know when you need their attention. This would work well in a situation where the kids are in a new, unusual and exciting environment which would make it difficult for them to concentrate on the teacher. The soprano range of a voice, even when positioned properly, is perceived as "high - excited" which might make the problem of communicating to overly stimulated kids even worse.
My client and I will continue to work on how he can position his voice so that he can do a full day of teaching without his voice getting tired. He's already well on his way.