Mechanisms accounting for the effects of mutually responsive orientation (MRO) at 7, 15, and 25 months in 102 mother–child and father–child dyads on child internalization and self-regulation at 52 months were examined. Two mediators at 38 months were tested: parental power assertion and child self-representation. For mother–child relationships, the causal pathway involving power assertion was supported for both outcomes. Diminished power assertion fully mediated beneficial effect of mother–child MRO on internalization and partially mediated its effect on self-regulation. For father–child relationships, MRO predicted self-regulation, but the mediational paths were unsupported. Paternal power assertion correlated negatively with both outcomes but was not a mediator. Although MRO with both parents correlated with child self-representation, and it correlated with self-regulation, this mediational path was unsupported.