There are substantial differences in language proficiency among children that are already evident in infancy. By kindergarten, this gap has widened: many children from disadvantaged backgrounds have fallen way behind their more advantaged peers in verbal and other cognitive and non-cognitive abilities, disparities that are predictive of later academic success or failure. Where do these differences come from? Language abilities are influenced to some extent by genetics, but aspects of early experience associated with socioeconomic status (SES) are also hugely influential—in particular, SES differences in the home language environment experienced by young children. Observational studies have shown that the sheer amount and quality of caregivers' verbal engagement with infants and toddlers are linked to later cognitive and non-cognitive outcomes and school success in both monolingual and bilingual children. This session presents new experimental research exploring the mechanisms that underlie these powerful effects of early experience on language learning, with the goal of examining their origins, consequences, and social policy implications from the diverse perspectives of neuroscience, psychology, linguistics, education, and economics. Understanding more deeply how early experience affects childrens', and thus nations', economic outcomes provides a scientific basis for more effective intervention and for innovation in public policy that will benefit children and, ultimately, nations.