Flexibility & Patience
There was a period of time when I worked with two prepubescent boys. Though I had previously taught a young boy who was already a professional stage actor, most of my students were from late high school age well into middle age and beyond.
I made an exception for these two boys because they were both performing locally and were very serious about their commitment to becoming theatre professionals. I did try to convince the parents to wait a couple years to start formal lessons, given how demoralizing to the ego the voice change can be.
I explained that for two to three years these boys wouldn’t know what sound was going to come out from moment to moment. However, both sets of parents thought it was preferable to slog through the instability and try to learn some basic skills rather than stop singing and wake up a couple years later with a voice they didn’t recognize and had no idea how to use.
So, I ignored the common wisdom of the time and, while the boys were still sopranos, I proceeded to work toward laying in some basic singing skills and awareness of the differences between one technical approach and another. I knew once the larynx began to drastically change size, all hell was going to break lose. And it did.
I had decided the best approach was to have different repertoire available depending on what voice showed up that day. We continued to work on the little boy music on the soprano days, and chose some appropriate baritone music for those days when their voices were in the lower octave.
This went on for the better part of two years. There were days, thankfully only for a short while, when we had to shift gears within a lesson, but once the voice change had been completed, both boys were singing quite well, with a good amount of usable repertoire in their new range. Most important, neither of them lost confidence or got confused -- something the parents were happy to have avoided by suggesting they keep studying.
The lesson here: Teach yourself and your students to be flexible and patient. It will pay off in the long run.