Some psychological peculiarities of adolescence as a particular phase in the psychological maturation (the phase of transition from childhood to adulthood) are considered. The author presents major developmental trends in adolescence, defines basic problems which have been studied in the experiments summed up in the paper, and suggests future lines of studying the principles of education of 10-16 years olds. Main attention is given to the problem of understanding the trends in the development of personality in the present day adolescents, as well as to the peculiarities of their self-consciousness and of their social activity.