The concept of the "zone of proximal development" is one of the influential aspects of the scientific work of Soviet psychologist Lev Vygotsky. Vygotsky explained that there exist within a person's zone of proximal development cognitive functions that are in the process of maturation but which are yet to be brought to fruition. As such, while a person's actual level of mental development is limited to the knowledge that she already possess, her proximal development refers to the cognitive capacities that she can be expected to have at some point in the future. The zone of proximal development involves the gap between a person's actual level of development as evident in her current ability to independently solve problems versus her potential level of development as evident in her ability to solve problems with the support and guidance of someone who has already mastered the material being learned.
The notion of the zone of proximal development challenges the current widespread reliance on standardized tests to assess student intelligence. Whereas such tests measure what students know at a given point, Vygotsky maintains that it is more important to evaluate students' independent problem-solving abilities and their potential for further development of these skills. After all, a person's capacity for solving problems on her own is likely to be a more important determinant of her lifetime success than the sheer quantity of knowledge that she might possess at any specific moment in time.