Laquitar - of course people use a range of techniques - nothing on the UP thread couldn't be used alongside other techniques, it's just another option. I think it's good if people want to mix and match :)
Squeaky - people have already said several times that preparing children for adulthood does not mean treating them like mini adults.
Maryz - it sounds like the book you were given was more about philosophy and less about how to implement it. Letting them make decisions doesn't mean you forfeit veto power over those decisions, however old they are, you are older and wiser - sometimes you have to use the knowledge you have to protect them. It depends what the outcome of their decision is likely to be though, you can protect them too much. Consequences happen anyway - if you don't brush your teeth, your breath smells which might mean you get teased at school, and you get an unpleasant feeling and taste in your mouth. You might decide though as an adult that if this natural consequence isn't making a difference or that it's not age appropriate, that the teeth need to be cleaned so they are going to be cleaned even if you won't do them yourself. Coming in late for a curfew means the curfew system isn't working, so we need a different system to keep you safe. So we find out why it isn't working - if it's just that it's an inconvenient time then perhaps we can negotiate a better time for everyone. Or perhaps it's non-negotiable, in which case, text reminders if it's a forgetting issue, or perhaps it turns out they can't be trusted with the responsibility of a curfew, so you sort out how they are getting home beforehand by picking them up or getting the friend's parent to drop them back (at 12-15 I'm guessing it will be parents) or booking a taxi in advance, if this isn't possible or they are managing to get around this then perhaps that's the time to decide you aren't responsible to be allowed out at night at all.
I know these things all sound like punishments, but that's a big misconception, that you can't do anything that even looks like a punishment in case it upsets the child. But no, in some cases it's necessary to do something which will upset them, for their own safety or wellbeing. The difference is that whatever you're doing has a direct result to achieving the desired outcome, so e.g. keeping them in instead of letting them out keeps them safe, whereas cutting pocket money or grounding them from another activity has no direct effect on their safety, which is the problem.
MollieO - not punishing/telling off does not mean not disciplining. To discipline = to teach. If you show them that paper is for drawing on, not walls, they seem to get the idea pretty quickly. If the behaviour persisted and they were old enough to understand then I'd probably progress to the lesson that writing doesn't come off walls easily, at any age, you can decide that they need supervision when using pens. When older I probably wouldn't correct spelling or grammar unless asked. (Assuming this is a separate issue)