After this presentation I see that presenting to a group of teens ages 10-16 surely is a task.  What helped the presentation was keeping the audience engaged by having them assist in the demonstrations.  I had one scout demo a trainer attached to a bike and challenged the scout to see how long he can peddle while I gave the demonstration.  Soon after every other scout wanted to participate in some way during the presentation.  To keep them engaged make it fun and challenge them.

http://lopeza.files.wordpress.com/2009/03/cycling.pdf