I have mixed feelings about teenagers and missions trips. And I've had mixed experiences. One observation is that because of a certain amount of immaturity, teens are subjected to special rules, which may in turn drive them to feel like less is expected of them because they are young.
On the flip-side, teens often lack a lot of the analyzing that we do as adults. I can remember being bolder about witnessing, because I wasn't worried so much about offending someone because of culture, religion, or otherwise. Again, it's both a plus and a minus.
I can remember a lot of occasions when my teenage peers and I displayed behavior that, when looking back, was not the best witness for Christ. The interesting thing about my situation was that the Russian camp staff watched me grow up, in a way. Although I was aware of being "set-apart," I still went through all the normal teenage struggles. But I was sincere in wanting to serve the Lord. Some of us hide our "ugliness" better than others, but we are all still being refined. As missionaries, our weaknesses are going to come out in one way or another. +/-