Every day there are more and more “methods” of training people to sing. There are brands and copyrights and merchandize and all sorts of claims put forth.
Any method of teaching singing is limited. It is limited by the person teaching it, by their life experience, their training, their interests and their own ability to sing. It is limited by their talent and their ability to communicate and by their understanding of how human beings make vocal sound.
Since functional training does not belong to any one person, method or approach, despite what some teachers would like you to think, all that can be done is to organize the material into some kind of cohesive whole that is accessible and useful to those who sing and wish to teach others to do so as well. A “method” is no better than it’s organizational factors. Those factors should allow complex information to be conveyed in a way that it is useful to a broad sector of interested parties.
The people who study any method are responsible for making sure they have clearly understood it before they use it. They are responsible for making sure that what they have taken away from the course is accurate, not only in relationship to the course itself, but to voice science and vocal health in general. They are responsible for staying in touch with those who hold the form of that method, adjusting to new information as it comes along.
If you are looking for someone to tell you how to teach singing and you want to be given complicated information that will require you to do exactly what someone else has thought of in the way that worked for them, and if you do not want to have to figure anything out on your own, you can certainly find such methods of teaching singing, as there are several that are popular all over the world. You can follow the premises of the founder of that method as if the founder was a genius who believed that he or she had found the holy of holies of teaching singing. If you want to be lead like a little sheep, it’s not hard to find methods of teaching singing that will regard you exactly in this manner.
If, however, you want to understand function and how it applies to you and to all other people who sing, you will not find all of that information in any method. You will need to read, study, attend conferences and congresses and immerse yourself in vocal study for a long time. If the person you have chosen to work with as your mentor is a valid expert, he or she will encourage you to do that and to look at a wide range of material in order to come to a deeper understanding of the teaching of singing. They will have no fear of what you will encounter in the wider world.
If, however, you find that the “method” you find most interesting does not help you in practical ways to be a better singer and teacher, no matter what that method claims to be or do, you need to keep looking, both at methods and at what you have learned or not learned. And, if the “method” you find keeps you stimulated, growing, expanding and enjoying what you do with your singing and your teaching, then dive deeply into it, plumb its depths and step up to the plate by sharing what you have learned with others. That which is solid, valid and practical will not go away, it will stand the test of time and of investigation.