I started playing at age 11, 11 years ago. So, while being five years later than your son, I still have some memories of what it was like back then. In the beginning, it's all about motivation. Really. There has to be something that makes your kid want to continue, indeed, a challenge. You don't want to be the Nazi dad, Murry Wilson or Joe Jackson style! The current teacher seems to provide that motivation. That being said, there should always be room for a bit of technical improvement. Just some few minutes every day before jumping onto the fun stuff would do wonders, and the earlier your son starts with those things things, the less problems he will have later on. I know people who started playing very early, always loved it, because their teacher is such an awesome guy. But, they never got their technique worked out properly; despite all the practising hours and the pleasure taken in playing, they had a hard time entering college; in that sense, all those playing hours led to nothing because they didn't lead to any mastering of the instrument.
I first started caring about technique when I was 16 or even 17. The professor I switched to had me drop everything else, and ONLY play etudes that seemed so fundamental it seemed silly to me. Needless to say, it worked wonders, because it was necessary. I had entered a school which sole purpose was to get their students into a an arts Uni, and it was a very challenging atmosphere, which made me take it seriously after a while. Had I been home I would perhaps not have cared so much. Can something like that be found for your son later on, I say shoot. Summer courses and camps are really important, too. For motivation, for the fun, and for taking things more seriously than is usually the case at home.
It can feel a bit awkward to change from a teacher you like, but in my experience, a new teacher always meant a huge leap forward. I've never played for the same teacher for more than two years, and I see no contraproductivity in that. Different teachers have different views, and in a couple of years they will perhaps not have made a star out of your son, but they've had plenty of time to etch their special points into the head of your son. The risk of having the same teacher for too long is that he will know what you'll sound like, and you'll know what he'll say, without it leading anywhere really. Of course, you can become the best of players studying for the same teacher all your life, but I say a change is a good thing, as long as it is to a good teacher. But, of course you have to talk it over with both your son and the teacher. I have yet to have a teacher who doesn't like the idea of me change to another, but I know there are examples of rather possessive teachers - as if they'd like to take credit on the account of their students' talent.
