how do you teach yoga to teens?  you start by teaching Truth.  speak to the highest in them.  they will get it when you tell them that they are a spiritual being in a physical body and that they are immeasurably powerful.   when they root their feet into their mat, into the earth in Mountain pose they will feel steady and strong; a steadiness they themselves create becomes a thing they can rely upon.  when their feet are rooted into the earth, they will become rooted in their integrity. when they are faced with difficult situations they can breathe into steadiness, root into their integrity and make grounded choices.