What a great question! A dancer asked me this at allexperts.com recently. And this was my answer:
"Having trained with Royal Academy, Cecchetti, French and Russian teachers I experienced contradictions in training. Yet I never felt any of my teachers were wrong.
When I started to teach, I chose whatever worked for each student, according to their physique. Unless, of course I was teaching Cecchetti for an exam."
I went on to remind her that classical technique defies anatomical norms. It is important that ballet instructors understand (whatever style) basic technique well enough to show students, individually, how to prevent injury on their physique.
Student can lose trust in a teacher because of the incorrect perception that a teacher doesn't know how to teach properly.
Some teachers are happy to state that their competitors teach technique incorrectly.
A kinesiologist will say most of ballet is downright harmful!
Another factor is that teachers may not express what they really mean very well.
Any student (of professional or recreational dance)can study the different ballet styles, and decide how they would apply the instruction to their physical type.
I advised her to get:
The Perfect Pointe Book - which demonstrates basic ballet movements
Tune Up Your Turnout - from a kinesiology perspective
Inside Ballet Technique -Separating Anatomical Fact from Fiction in the Ballet Class
Written by therapists and kinesiologists these are excellent guides as to what is "right", sans any style.
Every body is different, even the ones that are "creme de la creme" models chosen from among the "rest of us" at professional school auditions.
You need to know, and can find out, what is best for you. You want to achieve strength and grace which I wrote about in my article "Ballet - Ocean Waves - Fluidity".(It has a great video of fluid movement).
Enjoy your dancing!