Teens best teach each other. A teen climber is immediately enlisted in teaching climbing skills to the new climber when they have reached a certain level of climbing expertise. The act of teaching involves great amounts of trust and this bonds the climbers even closer together. Tree climbing can be introduced in many ways. It could appear as an after school program or you might attach tree climbing to the Physical Education curriculum during school hours.
Many high schools have their own outdoor adventure program.
This would make a good addition to the activities or it could be a stand alone activity if there was enough interest. An Explorers Post could also be established or tree climbing could be added to an existing program. There are many possibilities.