The current study examined the effects of parent–child and teacher–child relationships on behavior regulation of children at risk. In particular, the amplifying or attenuating effect of one context (i.e., teacher–child relationships) for another context (i.e., parent–child relationship) on children’s behavior regulation was examined. Participants were 291 children (159 boys) ages 37–70 months (M = 53.88 months, SD = 6.44 months) from three different preschools serving low-income children in two Midwestern cities. Parents and teachers reported on their relationships with children during fall. Behavior regulation was assessed via structured tasks during spring and summer. After controlling for demographic variables, results showed that parent–child closeness and teacher–child conflict were related to children’s behavior regulation. Interaction models showed that when children experienced a combination of low parent–child closeness and high teacher–child conflict, they had lower levels of behavior regulation. Findings highlight the importance of parent–child and teacher–child relationships, both independently and together, for low-income children’s behavior regulation.