The differentiation of two stages of mediation in interpsychic action (discovery and keeping of meaning stages), analysis of mutual succession of imagesymbolic and sign forms shows the limitations of traditional forming experiment: Practical activity organization corresponding to notion logics is only a part of action transition from adult to a child (during preschool-school change). The previous stage when the notion is made expressive by an adult makes it possible for a child to feel the meaning. This is not so far included in experimental-genetic method and forms its zone of nearest development.