As inequality increases in most developed countries, children from socioeconomically disadvantaged families are at exceptional risk for academic underachievement with lasting consequences for individuals, their communities, and society at large. Among policy makes, early childhood education and care (ECEC) is considered a key to remedy this risk. Yet the science on ECEC effectiveness at a national scale lags behind the excitement. Exploiting unique Norwegian data, we first seek to identify how and why socioeconomic disadvantage undermines children’s language skills and school achievement. Second, we will investigate whether ECEC can improve opportunities for disadvantaged children to excel. Third, to clarify the policy relevance of these inquiries, we will estimate costs of socioeconomic achievement gaps and the economic benefits of ECEC at scale. We take an investigative approach that is unprecedented in scope—from population level trends down to nuanced assessments of individual children’s growth. Throughout the 2000s, Norway’s child poverty rates increased from about 4% to 10%, while the coverage of public ECEC for toddlers increased from 30% to 80%. Across this unique window of time, we have access to rich survey data on language skills and home environment for 100,000 children, and genetically informative data, linked with administrative records on community- and family level socioeconomic risks and opportunities, and on national achievement test scores. These data allow us powerful analytic opportunities, combining state-of-the-art statistical, econometric, psychometric, and genetic epidemiological methods. I am well positioned to lead this project, having qualified for a Professorship at the University of Oslo aged 36, and having considerable experience in (a) publishing in highly respected scientific journals, (b) working at the intersection of research and policy, (c) leading research projects, and (d) mentoring younger scholars.