A dominant influence on the social constructivist paradigm is Lev Vygotsky's work on sociocultural learning, describing how interactions with adults, more capable peers, and cognitive tools are internalized to form mental constructs. "Zone of Proximal Development" (ZPD) is a term Vygotsky used to characterize an individual's mental development. He believed the task individuals can do on their own do not give a complete understanding of their mental development. He originally defined the ZPD as “the distance between the actual developmental 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.” He cited a famous example to make his case. Two children in school who originally can solve problems at an eight-year-old developmental level (that is, typical for children who were age 8), might be at different developmental levels. If each child received assistance from an adult, one was able to perform at a nine-year-old level and one was able to perform at a twelve-year-old level. He said “This difference between twelve and eight, or between nine and eight, is what we call "the zone of proximal development."” He further said that the ZPD “defines those functions that have not yet matured but are in the process of maturation, functions that will mature tomorrow but are currently in an embryonic state.” The zone is bracketed by the learner's current ability and the ability they can achieve with the aid of an instructor of some capacity.