How do you know if a brass development method "works?"
Most people would say, "you get better." But the problem is, such an idea fails to take into account that some players simply get better by practicing almost anything. How is it possible to be sure that a particular method is the difference maker?
Here is a big clue: Look at players who struggle the most. In my experience, players with chronic embouchure inefficiencies do not get better by general practice. If you can find clear evidence which supports the claim that a wide variety of players with chronic difficulties - who struggled for years with different methods - have gone down a specific path and successfully pulled themselves out of the mud, then you have the most compelling proof available that a particular method is responsible for the difference.
Another clue is to look at players who have stopped improving. Although reluctant to admit it, a lot of professionals are in this category, stuck on a plateau for years, unable to improve. If a single method causes improvement to start again, then it must be considered as reasonable proof of the efficacy of the method.
The above is taken from Jeff Smiley's website. Jeff has listed many great testimonials, which you can find here: www.trumpetteacher.net/testimonials.html