Where to? georgemuresan/iStock via Getty Images PlusAs tourists head to airports this summer, American travelers are likely to see groups of young people in matching T-shirts awaiting flights to Latin America or further afield. Their T-shirts sport biblical verses or phrases like “Here I am, send me” or “Called to serve,” and the teens may gather for prayer before boarding. These young people are heading off to be short-term missionaries: an experience that has become a rite of passage in some c