Since the Coleman Report's release in 1966, education policymakers have grappled with the fact that, on average, African American children's academic and behavioral outcomes are depressed relative to those of white children (Coleman et al. 1966). Because African American children disproportionately come from low-income families, it is generally understood that the disadvantaged social and economic conditions from which many of these children come to school predict these depressed outcomes. "Stress" is a commonplace term for hormonal changes that occur in response to frightening or threatening events or conditions. When severe, these changes are termed "toxic" stress and can impede children's behavior, cognitive capacity, and emotional and physical health. Frightening or threatening situations are more sustained and are experienced more frequently by African American and socially and economically disadvantaged children, who also have less access to protective resources that can mitigate their stress to tolerable levels. Seeking to improve outcomes for these children, education reform efforts have focused mostly on how higher-quality teaching can overcome the force of social and economic challenges; however, these efforts have failed to make a meaningful dent in the black-white achievement gap. This report describes the relative frequency of toxic stress by race and social class, and shows how it depresses children's outcomes and contributes to the "achievement gap." It concludes by suggesting policy and practice recommendations that can reduce the cognitive, behavioral, and health harm that toxic stress provokes. [This report was produced in collaboration with the Opportunity Institute.]