Humanity is young: In 2006, over a third (2.2 billion) were under age 18 and almost half were under age 25. In addition, nearly the majority of young people ages 15–24 lives on less than $2 per day, 15 percent are undernourished, and 14.4 percent are unemployed. Although 85 percent of young people live in developing countries, only a fraction of adolescent development and mental health research is focused there. Efforts to shift the emphasis of such research also must engage with the prevailing views in development theory and policy that link human development with socioeconomic development in a “dual development model.” A critical cultural analysis of this model reveals both the bases and limitations of its power, and identifies an implicit cultural model of the life course within it. The model mandates society-to-individual (outside-in) investments in health and education that are expected to return reciprocal gains in lifetime productivity that benefit society as a whole (inside-out). The current burden and advantage of this equation are assessed as they bear on young people across the globe. A case is made for lifecourse cultural models as a potent framework for mediating among realities, perceptions, and behaviors at the level of youth, parents, and policies under conditions of rapid culture change.