Jean Piaget and Lev Vygotsky\

Vygotsky approached development differently from Piaget. Piaget believed that cognitive development consists of four main periods of cognitive growth: sensorimotor, preoperational, concrete operations, and formal operations (Saettler, 331). Piaget's theory suggests that development has an endpoint in goal. Vygotsky, in contrast, believed that development is a process that should be analyzed, instead of a product to be obtained. According to Vygotsky, the development process that begins at birth and continues until death is too complex to to be defined by stages (Driscoll, 1994; Hausfather,1996).
Vygotsky believed that this life long process of development was dependent on social interaction and that social learning actually leads to cognitive development. This phenomena is called the Zone of Proximal Development . Vygotsky describes it as "the distance between the actual development level as determined by independent problem solving and the level of potential development as determined through problem solving under adult guidance or in collaboration with more capable peers" (Vygotsky, 1978).

Other sites of interest. L VYGOTSKY,
http://tip.psychology.org/piaget.html
Characteristics of Constructivist Learning & Teaching
Piaget's Theory of Cognitive Development.
Piaget power point