There is a sizable gap in school performance by gender and socioeconomic status, favoring girls and children of parents of higher socioeconomic status. These gaps open early in life, are persistent throughout childhood and adolescence, and may manifest into negative consequences later in life. The Childhood Gap project aims to improve our understanding of the causes, and consequences of these early childhood inequalities, and to inform the design of policies aimed at diminishing or closing these gaps. The Childhood Gap will advance the research frontier by conducting a large-scale study that will follow three cohorts of children over time, combining surveys, lab experiments, and administrative data. We will conduct a detailed mapping of childhood development by collecting data on the children, their parents, siblings, peers and teachers.