Hmmm, as an errant teen myself (dated a man more than twice my age, dissappeared overnight regularly etc, truanting-although was college age by then), I would say that I always look back and wonder why my parents weren't more strict.
I haven't reached this stage with my own children yet, so may well change my mind when I get there!
However, my parents were quite straight and I had that typical teen view that they just didn't understand. They I know, were afraid of alienating me and so chose the middle ground. This meant they occasionally confronted me gently, but usually pussyfooted around me (poor things, I was horrid).
I grew up in a nice stable home as yours sounds to be, and honestly have no idea why I behaved in the way I did.
I think that if they had really laid the law down, I would have obeyed, being a good girl at heart too.
BUT, I don't know wha could have been done about the truanting. It wasn't that I didn't like school, I was very academic, but more that I couldn't cope with it emotionally- again no idea why, it just overwhelmed me somehow.
This is partly to do with personality I think- traditional education doesn't suit everyone and socially it can be difficult. And to this day I avoid administration of all sorts if possible.
For me it was also to do with the company I was keeping, ie the older man. The world was a very bewildering place for me back then, I think even more so because I came from a nice family and so emotionally was probably pretty sheltered and naive.
I'm not sure what I'm trying to say other than I believe it would have been better for me if my parents had laid the law down and stuck to it. They didn't restrict my activites or take away anything I loved (we had horses) for fear of hurting me, but they should have done. I would have hated them for a while, but it wouldn't have lasted long, and the repercussions of the continuation of my behaviour were huge.
This is obviously a very personal point of view, and even though I have been there, I can't explain what the reasons were. I can only say that I was fiercly independent with no idea how to be.
Sorry for the long post, hope things are ok