This paper discusses a class of phenomena called a "responsible decision", a type of decision making in which the choice between behavioural capabilities is determined by the alternative values that lie behind them. Using Vygotksy's theory of cultural and historical development, this paper posits that the process of a child's internalization of interpersonal dialogue is used as a means of making a responsible decision. The participants in the study included 137 Russian children and adolescents, aged 6-17 years old. The procedure used in the study showed an increase in the level of maturity of responsible decisions in children aged 6-11-year-old. The study revealed that the primary school age is the crucial time and area of proximal development for making responsible decisions. This has implications for some of the methods which adults can use to support a child's ability to make responsible decisions.