The relation of reflection-impulsivity and motor inhibition to naturally occurring social and self-regulatory behavior of 121 urban Head Start boys and girls was examined. Correlations between the Kansas Reflection-Impulsivity Scale for Preschoolers, motor inhibition tasks, and classroom behavior were computed for two groups of Head Start classes that differed in race and the amount of adult-imposed classroom structure. In the less structured classes, impulsive children were less aggressive, less assertive, and less likely to show understanding of others or to engage in such prosocial behavior as cooperation, helping, and sharing than were their reflective peers. Impulsive children were higher than reflectives on two indices of self-regulation: responsibility during clean-up time and waiting patiently during delays. Impulsivity was not related to behavior in highly structured classes. Motor inhibition was not consistently related to the observational measures.