Russian followers of Vygotsky have elaborated his theoretical ideas into a logical and internally consistent activity theory of child development, which integrates cognitive, motivational, and social aspects of child development with an emphasis on the role of children's activity in their development. To highlight the innovative features of the neo-Vygotskian activity theory, it is worthwhile to compare this theory with the theories of child development of Vygotsky and Piaget, even though such a comparison will involve some repetition of already-discussed issues.

In Piaget's (1936/1952) theory, the major determinant of children's cognitive development is their independent activity aimed at the exploration of the external world, which leads to the formation of children's mental procedures (schemas). This explanation of the determinant of child development stresses the role of children as active contributors to their cognitive development but undermines the role of social environment in child development. In contrast to Piaget, Vygotsky (1978, 1981a, 1934/1986) stressed the role of social environment in child development. In his theory, adult mediation (that is, supplying children with new psychological tools and the organization of the process of their acquisition and mastery of these tools) is considered the major determinant of children's development. Vygotsky, however, defined psychological tools as semiotic tools rather than as mental procedures. Also, he was not consistent in his views on the role of children's activity in their development, sometimes describing mediation as the process of assimilation by children of semiotic tools presented to them by adults in the course of interpersonal communication.