I have had the great pleasure to teach many teenagers and it is by far one of the most challenging things I have done. The challenge lays in many aspects.
The rare times I haven't enjoyed teaching teenagers was when they were forced to come to a dance workshop. I would arrive in a school and have to lead a creative workshop and find out that most of the students didn't know I was coming or had no wish to discover something new. At first I spent the whole workshop trying to get them to do something the way I had planned it but it never really worked. I would often end up with my voice and my energy gone and with a very poor result. I decided to change drastically what I was doing.
The most difficult thing is the beginning. Trying to have them face the same direction and then learn even a small exercise doesn't work. It is far more efficient to have them follow your lead and copy you as best they can. I include all the things I want them to do (weight transfer, pliés, using the breath, etc) but without really mentioning it. I never use any technical terms such as pliés, demi-pointes, etc.
The warm up is now very quick and energetic. A bit like dance on the verge of becoming fitness. I found as well that it is best not to bring attention to a single one of them to soon. So I avoid the "Let's watch Jessy cause she is doing it very well!" sort of thing (under 12 love doing that).
Once they are warm I usually start a creative task but I talk about it in very specific terms. The word "improvisation" doesn't really work. They find it very scary so I replace it by "Moving around" which may seems a bit degrading but it doesn't last long because once they get comfortable with the task I quickly tell them that what they are doing is improvising.
Obviously this is for teenage first timers. I am describing a one off workshop situation, not a group taught on a regular basis. Although I think quite a lot of things can be applied to both.
One of the major things with teens, whether new to dance or not, is the relationship that they have with their bodies, particularly girls. Their bodies are changing fast and they're not comfortable with all these new features. (hair, breasts, spots, etc) So I try not to give creative tasks that use the body as an instrument (measuring space with your limbs, folding unfolding your body into the space, writing your name, etc) but tasks that bring their attention to the outside world (reacting to a colour or picture, copying someone, expressing a feeling, etc).
I haven't had the chance yet to follow the same group for a long time. I have only done it twice, teaching in a dance school for future pros. The thing that I particularly enjoyed was their speed at learning everything. I was able to witness their progress during six months. Of course they were taught all day, everyday, so it is normal to progress fast. But it is something I started noticing in one off workshops as well. The notion (weigh, quality, rhythm, etc) I concentrated on during the workshop felt learnt, more so than with younger groups.
I find that when a teenager is willing to learn, he or she can do it faster than others. The younger ones are not ready yet. I really like Jean Piaget's stages (see Wikipedia) :
-Preoperational stage: from ages 2 to 7 Acquisition of motor skills. Children cannot conserve or use logical thinking.
-Concrete operational stage: from ages 7 to 12 children begin to think logically but are very concrete in their thinking. Children can now conceive and think logically but only with practical aids.
-Formal operational stage: from 12 onwards. Development of abstract reasoning. Children develop abstract thoughts and can easily conceive and think logically in their mind.
To finish I will just say that every time I look into studies about teenagers I find out more. It is a fascinating subject. I am not a specialist on the subject. Please leave some comments and share your experiences on teaching.