Of the 1.2 billion adolescents in the world today, 90% live in low- and middle-income countries. These adolescents face many challenges in their lives. Enrollment in secondary schools is still low in many parts of the world, with illiteracy rates approaching 30% in the least developed countries. Further, adolescents not in school are more vulnerable to trafficking, recruitment into armed conflict, and child labor. Many adolescent girls marry and begin...