This study compared the conversations between a mother and her children, and a father and his children as observed in the film Boyhood to examine the mirroring effect in communication. The children’s conversation styles exhibit aspects that are similar to those of their parents, like a mirror of their parents’ conversation style. The parent-child conversation style influences the formation of children’s self-concept. The parent–child conversations in the film were qualitatively analyzed using you-messages and I-messages, as suggested by Gorden (1975). Furthermore, based on the components of youmessages and I-messages the number of statements in the parent–child conversations was quantitatively analyzed into different factors. The analysis revealed that the parent-child conversation style manifests mirroring-like aspects in the children’s conversation style, and that this mirror-like aspect influences the formation of children’s self-concept. The results of this study are as follows. First, through the analysis of the mother-child and father-child conversations observed in the film Boyhood, the study demonstrated that communication between individuals has a mirroring effect. Second, it demonstrated that the parentchild communication style is closely associated with the children’s self-concept formation using self-concept and the P.E.T. (Parent Effectiveness Training) theory. Third, parents are ‘significant others’ and play a key role in forming their children’s self-concept. Therefore, the study suggests that it is necessary to apply positive communication methods more frequently to guide the development of children’s self-concept in a more positive direction.