The global commitments made at the turn of the Millennium – to end poverty and hunger, improve access to clean water, sanitation and basic health care, and to expand primary school enrolment – were intended to transform the lives of children. Longitudinal studies that have tracked the lives of children over this period, have lessons to share as the world embarks on new commitments to an ambitious sustainable development agenda.

Drawing on findings from Young Lives, this Brief illustrates the unique advantages of tracking cohorts of children over time to understand causes and consequences, the dynamics of change and the interaction between complex factors in determining outcomes for children. It offers lessons that can inform timely and effective policy responses to changing circumstances, as well as point to some data needs, for the next 15 years and beyond.