The 2017 Lancet Series, Advancing Early Childhood Development: From Science to Scale, estimated that 43% of children under 5 years in LMICs (250m children), were at risk of not reaching their potential because they had stunted linear growth or lived in extreme poverty. The proportion of children at risk increases appreciably when additional risk factors are considered, especially low maternal schooling and child maltreatment. Living in poor and unstimulating conditions affects young children's learning and development. Children exposed to poverty and adversity explore and learn less than children not exposed to these stresses, they learn less at school and achieve fewer school grades, earn less as adults, have more social problems, and poorer physical and mental health. We will study barriers and accelerators to learning in LMIC ECE programmes, at home and in communities, as well as associations between early learning and indicators of child development and  school performance. We will estimate their longer-term effects on education and earnings in adulthood. We will use descriptive and statistical analyses of secondary data collected through representative country surveys and research studies. As an established group of multi-disciplinary and multi-country experts and collaborators, we build on prior success in sourcing and analysing data from 91 LMICs by including early education and expanding to 137 countries. Global data, presented along the continuum of the early years, breaks down the false dichotomy between ECD and ECE, between care and education, and between learning at home and in formal programmes, and supports multi-sectoral actions along different stages of the life-course. We will expand our global analyses of threats to ECD by examining gender, location and wealth, services and family supports for young children, and policies that create facilitating environments for families and children. We will, for the first time, link indicators of the structural quality of ECE (eg teacher-child ratios) to contexts and child outcomes in LMICs. Process quality (eg teacher- and caregiver-child interactions), on which there is as yet no global data, will be studied through case studies in 5 countries, one in each of five regions of the world. We will source data on government, development assistance and household expenditures on pre-primary education, extract further country micro-data on contexts in which young children develop and learn, update nationally representative data on young children, services and policies to the most recent survey dates available, and develop new composite indicators of barriers and accelerators of young children's learning and development. Through partnerships with regional networks of ECD-ECE government and stakeholder teams, the project will help to build research capacity in ECD-ECE, and increase the use of data for decision-making, action and monitoring in 20 countries. We will use the results to provide evidence-