Longitudinal study is focused on inter- and intra-subject factors that define the dynamics of social formation during maturity, i.e. the period from the primary school age to the age of early adulthood. Inter-subject factors are considered to be the conditions of educational environment created in the course of the pedagogical experiment. Features of human mental representation of him/herself and the world are defined in the study as intra-subject factors. The longitudinal study, which continued for 18 years, has been conducted in several directions: the comparison of the two phases of the study; intra-individual analysis of the dynamics of participants’ social development; defining the stability a person’s self-representation in a long-term perspective.

The first part of the study represents the typical age group «points» of social development, the development of one’s identification with humanity («I - person») in particular. It is typical for a 7-9 year old to experience the lack of “I-person” identity; during adolescence there are two coexisting images in the mental self-representation: «I» and «Person»; by the age of 25 the «I - person» identity is formed by approximately 40% young people. It has been discovered that specially organized pedagogical conditions contribute to the actualization of identification with the human community; moreover, under certain conditions the «I - person» identity of can be actualized at the primary school age. The age of 7-8 years is considered to be the sensitive period for the formation of social identity. Once formed the identity appears to be stable, and retains for the coming decades.

The second part represents the analysis of the specificity of mental self-representation’s effect on the subsequent social and psychological development of a person. This approach allows to distinguish the directions of social maturity development and to describe empirical intra-subject ways to form social maturity between 7-25 years.

The results have theoretical significance for the developmental psychology and educational psychology. They aim is to create the periodization of person’s social development; define sensitive periods of social identity in the mental representation that contributes to social and personal maturity, and also psychological health. Identified patterns can be used in social development of elementary school, which should be based on inter-subject factors of social maturity.