I've been both a student and a leader -- highly recommend Global Routes

When I was 17 I traveled with this organization to do traveling theater in Europe (a program that no longer exists). It was one of the most influential, life changing experiences of my life to that point. It was instrumental in me developing the values that I have today (and really making me cognizent of living those values). The organization emphasizes personal growth, development, and leadership. They take you out of your comfort zone just enough to be a challenge and still fun.

In my 20s, I came back to the program as a leader. All leaders are trained in experiential education, and are selected from a large, qualified pool of talented applicants. They work hard to make sure everyone has a good time, and that everyone is accepted and met (and challenged) at their level.

Global Routes is a fantastic organization. If you're thinking about a summer travel program for teens, they should definitely be at or near the top of your list.