Education is essential to prepare adolescent girls for healthy, safe and productive transitions to adulthood. However, adolescent girls in much of the developing world are underserved by the education sector – too many are not in school, or are not receiving a quality, relevant education in a safe and supportive environment. At the same time, programs that emphasize girls’ healthy and productive transitions to adulthood are not adequately linking with the education sector. Despite the common goals held by sectors that serve adolescent girls – from education to reproductive health to economic development – their strategies are fragmented, and they do not reach girls at an adequate scale. This paper makes a case for why leveraging education to facilitate girls’ transitions to healthy, safe and productive adulthood is the single most important development investment that can be made. We provide guidance on how we can build on past progress, forge more productive alliances and redouble our efforts to ensure that all girls in the developing world have the opportunity to obtain a quality, relevant education. In order to do this, development practice must shift to accommodate and facilitate cross-sectoral collaboration for girls’ healthy transitions to adulthood. With a shared vision, and coordinated strategies to achieve that vision, sectors ranging from education to health to economic development can contribute to a whole that is greater than the sum of their parts.