Thesis: Ph. D., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 129-170).Adults greatly impact children's learning: they serve as models of how to behave, and as parents, provide the larger social context in which children grow up. This thesis explores how adults impact children's learning across two time scales. Chapters 2 and 3 ask how a brief exposure to an adult model impacts children's moment-to-moment approach towards learning, and Chapters 4 and 5 look at how children's long-term social context impacts their brain development and capacity to learn. In Chapter 2, I show that preschool-age children integrate information from adults' actions, outcomes, and testimony to decide how hard to try on novel tasks. Children persist the longest when adults practice what they preach: saying they value effort, or giving children a pep talk, in conjunction with demonstrating effortful success on their own task. Chapter 3 demonstrates that social learning about effort is present in the first year of life and generalizes across tasks. In Chapter 4, I find that adolescents' long-term social environments have a selective impact on neural structure and function: socioeconomic-status (SES) relates to hippocampal-prefrontal declarative memory, but not striatal-dependent procedural memory. Finally, in Chapter 5 I demonstrate that the neural correlates of fluid reasoning differ by SES, suggesting that positive brain development varies by early life environment. Collectively, this work elucidates both the malleable social factors that positively impact children's learning and the unique neural and cognitive adaptations that children develop in response to adverse environments.by Julia Anne Leonard.Ph. D.