davidmazon

From what I have noticed with my students: We start with a 7c. Once the breathing is free and correct, I listen for the sound difference between a "right above the staff" g and the low c below the staff. If the tone quality is the same(most of the time it is not..most younger players sound's will change to a pinch which means the breathing is incorrect) I then listen for ...its hard to describe...the "stuffiness" sound(related to a voice its almost like when you tighten your abs and try to talk). If it is there we try some bigger pieces, if not we don't:). I have seen some students not need to change to a bigger piece(unfortunately) and some that really had a hold of breathing need bigger pieces very quickly.
My personal opinion of a 5c mouthpiece: should not be played by beginners. Pretty difficult piece(flat rim, sharper bite, more cup shaped).
The mpc sequences for students that I have found work the best are:
7C, 3C, 1.25C (only for college players do we start messing with throats and backbores unless the student is an absolute monster)
5C, 5B, 3C, 1.5C
You can insert yamaha equivalents as needed! The 16C4 GP is a great mouthpiece but it is more important for the student to learn how to fill the mpcs with the correct amount of air before messing around with bigger sizes. Breathing is the most important thing. I myself am a mpc crazed nut but the correct mouthpiece for a developing student is such an important issue it must be addressed with the knowledge of a competent teacher who's best interest is developing a great trumpet player (there are some nuts in Columbus Ohio who start kids on 14a4as..yikes).
Good luck and hope my opinions help!