Children living in food-insecure households face myriad challenges to their well-being. The Great Recession of December 2007–June 2009 increased food insecurity to the highest levels ever measured in the United States. Using nationally representative data from the period 2010–12 for 6,300 children in the Early Childhood Longitudinal Study, Kindergarten Class of 2010–11, with household incomes below 300 percent of the federal poverty level and a dynamic measure of food insecurity transitions, we assessed the impact of transitions into and out of household food insecurity on the academic achievement, behavioral problems, and health status of young children. We found negligible impacts of food insecurity transitions on academic achievement in first grade. However, we found consistent negative impacts of the transitions on teachers’ reports of children’s externalizing behaviors, self-control, and interpersonal skills and on parents’ reports of children’s overall health status. Taken together, our findings underline the importance of food security for children’s healthy development.