The first part of the paper describes an approach to understanding social maturity and operational criteria for its estimation. In general, social maturity is defined as the willingness of an individual to take responsibility for developing his/her community. Social identification with broad social communities is an integral component of social maturity. The paper presents the results of the age analysis (intra-subject factor) and the analysis of psycho-pedagogical conditions (inter-subject factor) which facilitate the appearance of «I - person» social identity in the mental representation of a person. Inter-individual trajectory of social maturity development passes through a number of «points». At the age of 7 a person has a typical position of «I» identity; during adolescence the teenager reaches the point of the «Person» identity, whose qualities may differ from those of a child. By the age of 25 more than third of young people has acquired the «I-person» identity. Recreation of psycho-pedagogical conditions in primary schools, development of children’s cooperation, development of children’s ability to communicate with different participants of the educational process, actualization of different levels of social identity are the factors that allow to found the basis of the «I - person» identity in two thirds of the participants of the experiment. The results are stable over a long period of time (18-year).

The second part represents the analysis of the specific features of mental self-representation effect on the subsequent social and psychological development of a person. Correlation analysis between the indices of the categorical structure of texts written on the same issue by the same authors at the age of 7 and then 25 years has revealed the types of empirical ways to form social maturity. These types include: «I - for the Company», «I – for others», «I - for the family,» «I –for an activity» and «I - for myself.» The ways to form social maturity are widely shown in the paper according to these types.

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.