The effect of maternal personality characteristics and interaction behavior on interventions with children was investigated among 210 Puerto Rican mother/child dyads of low socioeconomic status. Mothers' and children's personality characteristics were assessed according to numerous and varied paper-and-pencil tests. Measures of children's performance included four aspects of role playing and nine dimensions of ego functioning; measures of mothers included aspects of personality orientation and level of ego development. Additionally, (1) each child's mother and teacher were asked to evaluate the child on several measures, (2) mother/child interaction was assessed by direct observation in a treatment analog, (3) each mother was pretested and posttested, and (4) a subgroup of 40 mothers participated in a videotaped structured interaction task. Findings generally indicated that the mother's ego development level, self-regard, self-acceptance, acceptance of aggression, and trait anxiety were related to the child's relationships with others and to the development of more adaptive person relations. (RH)