I quit for a few reasons:
1) I didn't like the teacher much. Too much "well if you don't learn what I think you should learn first, then you won't be able to play what you want to play". IMO that is a bunch of malarkey. If there's something that excites you to learn, a teacher should incorporate the piece and the excitement into teaching fundamentals. In fact, I learned on my own as I do with all my instruments because of this very reason.
2) I was young and impressionable and thought the piano was a "girls" instrument. Had my teacher helped me learn the songs I was interested in as opposed to "Medieval Dance" perhaps I would not have been so easily coaxed into that prejudice.
Sounds like the teacher is kind of jerky - and if I may assume, your son may also be suffering from unjustified pressure to play a more manly instrument. Ask him to learn a song of his own accord and see if that sparks new interest.