PROJECT SUMMARY/ABSTRACT In the United States, children’s development differs markedly as a function of their family’s socioeconomic status (SES). Some of the most pronounced and consequential SES disparities are in language and cognitive development, which are evident as early as two years of age and, by kindergarten entry, predict with depressing accuracy children’s long-term academic trajectories. Yet while social science has identified a variety of structural, contextual, and psychological factors that contribute to disparities in child development, we have limited understanding of how these factors “get under the skin” to influence biological processes that are proximally involved in brain maturation and shape key developmental outcomes. This proposal integrates approaches to understanding developmental disparities from the biological and psychological sciences. Theorists in the biological sciences have proposed that disadvantage gets biologically embedded during gestation, in part via immune responses to stress that result in “adverse gestational environments” (AGEs). Animal studies have confirmed that stressful exposures can contribute to adverse gestational environments and to subsequent oxidative neuronal injury and impaired development, yet human studies have yet to examine whether AGEs are associated with socioeconomic disparities in language and cognition. We leverage an existing NIH-funded study of disparities in perinatal outcomes, where in-depth assessments of SES and the gestational environment are being performed in 600 pregnant individuals from diverse backgrounds. We will follow children born to these individuals, collecting measures of cognitive and language development during the infant-toddler period as well as preschool outcomes at age 5 years. Aim 1 will determine if adverse gestational environments resulting from maternal stress mediate socioeconomic disparities in child language and cognitive development. Aim 2 will deepen understanding into the placental characteristics of adverse gestational environments that are associated with lower language and cognitive development. Aim 3 will examine the combined contributions of AGEs and postnatal caregiving environments in predicting language and cognitive development. Across these aims, we utilize state-of-the-art methods from the social, behavioral, and biological sciences, and adopt a culturally and linguistically responsive approach to assessment of child language and cognitive development. This study will answer key questions about the origins of SES disparities in language and cognitive development that have important implications for theory, policy, and practice.