The essence of man's social development consists in his individual development, its goal, highest stage, and end product is the appearance of personality. Therefore in the study of mechanisms and conditions of the personality formation the most important place belongs to the research concerning specificity and stages in the social development of a growing man. Different degrees of the latter process are related with different stages of the ontogenesis. They are marked with clear-cut boundaries where the achieved results of the social development are fixed. Two types of such boundaries are distinguished intermediate and nodal. Those of the first type correspond to a child's transition from one ontogenetical period into another. The nodal boundaries signify qualitative shifts in the social development. Three stages of the social development process are outlined, as well as both inter and intra-stage mechanisms of personality formation.