This study was developed to investigate an influence on a social reaction and pattern of communication of the little child within a mixed age group, supporting the previous studies which a mixed age group could have an important effect upon a social recognition development of the little child. A sampling frame of this study was obtained from 2 of a full three, four and five years old respectively who had lived together with other age group. This study was intended to provide explanation for the method of how the older little child had a proximity effect upon development to the younger little child and how the interrelationship of a group of that age who the age and the characteristic of their development were about the same in positive or negative social reactions had an effect on development to the other. This study was investigated based on a theory of Vygotsky centering around the patter of responsibility, collaboration, social reaction, self-confidence and perceptive communication which the little child could show in reciprocal action. A sampling group and hypothesis were established in this study as follows. Study 1. What difference was shown in a social reaction of the little child according to experience of a mixed age group? hypothesis 1-1.The little child who took a common task could take a higher point on pro-society check than the little child who didn\'t take a common task. 1-2.The little child who took a common task could take a higer point on alternative thinking faculty of solution than the little child who didn\'t take a common task. 1-3.The little child who took a common task could grow into adulthood taking a common task in their social reaction. Study 2. What difference could be shown in a pattern of communication when they were taking a common task in a mixed age group? Hypothesis 2-1.The pattern of communication could be changed when the little child in a mixed age group were taking a common task on development program of their life in society as the number of program got increased. 2-2.The pattern of communication of the little child who took a common task in a mixed age group could be different according to their age. The results of this study are summarized as follows. In a change of social reaction of the little child according to whether they experienced a mixed age group or not, First, the check points on a pro-society activity of a full three, four and five years old who took a common task were changed than the little child who didn\'t take a common task(t=2.41, p<.05). Second, hypothesis which their social reaction could grow into adulthood as the little child who took a common task were taking a common program on development of their life in society was supported by this study. The cases indicated their social reaction could be changed to grow into adulthood ① from non-related to offensive reaction(from unsettled non-related to negative settlement), ② from offensive to pro-society(from negative to positive settlement) after they took a common task. A change of communication was investigated as they were taking a common task in a mixed age group. Third, a hypothesis which the pat tern of communication of the little child could be changed as the little child were taking a common task on development of their life in society in a mixed age group was supported by this study.