The purpose of this study is to explore the most appropriate ratio of teacher vs. children in a childcare and a kindergarten class. This issue is one of the core requirements for quality education and care. For this research, we studied on characteristics of reciprocal functioning in teacher-child relationship, current state of teacher-child ratio, and review of other countries’ criteria of adult-child ratio. Based on these results of study, we also suggested appropriate ratio of children vs. teachers and discussed about strategies for improving policies. The methods we employed in this study are to review literatures, to investigate 269 experts’ opinion, observation of reciprocal activity in classes(case studies), interview with teachers, and visiting sites and interviewing with providers in foreign countries such as Denmark and Scotland. In conclusion, we suggested four different ideas on adjusting current national criteria of teacher-child ratio based on the results from the various research methods: a) a new criteria of ratio in each age group, b) criteria of class size and additional personnels, c) a new approach to defining age groups, and d) the way to improving current national criteria. In addition, we calculated anticipated budget for each idea.