The paper discusses differences between types of the leading activity relating to the systems "the child - the social adult", "the child - the social object", describing and analyzing situations and specific actions characteristic of both systems. The systems were introduced by D.B. Elkonin. The author argues that in activities belonging to the "child - social object" type there is a distinction between the natural and the cultural (artificial) action and the distinction mechanism is a specially organized trial action with a special culturally constructed object. In activities of the "child - social adult" type the developmental mechanism is a complete reconstruction of activity situations in which the agent discovers his own feelings. The above developmental mechanisms are discussed in terms of scientific and artistic modeling.