This brief presents the findings of a study that examined the effects of "allostatic load" on children in poverty at age 9 and 13. "Allostatic load" refers to the measurement of the cumulative wear and tear on the body that results from experiencing stress. Research shows that high allostatic load in childhood is associated with long-term vulnerability to poor health and mental health outcomes, and that these effects begin early in life. In this longitudinal study, 207 children from a poor rural community were studied first when they were 9 years old, and again four years later when they were 13. At both of these points, the allostatic load of each child was measured using a combination of several physiological assessments associated with physical stress, including resting blood pressure; overnight assessments of stress hormones cortisol, epinephrine, and norepinephrine; and a measure of body fat. The results of this study indicate that, for children, chronic stress gets built into the body, and its cumulative effects are linked to increased physiological risk of long-term health problems. Findings regarding the effects of allostatic load provide a link between adverse environments and impaired reactions to stress, greater behavioral problems, and poorer academic achievement.