The zone of proximal development

The zone of proximal development, or ZPD, is defined as the interactional space where a learner is able to perform a task with help which is beyond his or her current level of competence alone: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. (Vygotsky, 1978)

Vygotsky considered this level of potential development to be a better indicator of a learner's competence, and later educators have seen the ZPD as an ideal locus for successful teaching