I posted on the TES website about dd's recorder "lessons" at school. I was basically asking if I should mention that she had been taught to play F the cheating way. The general consensus was it doesn't matter.
As she had to play the note for a piece in the EAster assembly I let it go but made sure she knew how it SHOULD be played (she wasn;t capable of using the little finger). It also appears that she is the only one who tongues as I began teaching her before she started at school.
It was a real bugbear of mine but she enjpoys taking part in the school recorder events so I just have to do what I can at home to counteract the bad technique at school.
To get back to the OP, dh is a peripateic and private teacher. He charges £25 per hour to teach from home and £30 per hour in schools (to account for the travel).
Teaching is his vocation.