The main difference between piaget's theory and vygotsky's theory of development is that: question 3 options: 1) the stages of cognitive development in vygotsky's theory occur at much earlier ages than the corresponding stages in piaget's theory. 2) piaget stressed the child's independent discoveries, whereas vygotsky stressed that supportive interactions with parents and others played a key role in cognitive development. 3) vygotsky stressed the independent efforts of the child, whereas piaget stressed formal learning experiences. 4) vygotsky's theory supplied additional evidence for piaget's conclusions.