Zone of proximal development

Lev Vygotsky's notion of zone of proximal development (зона ближайшего развития), often abbreviated ZPD, is the gap between a learner's current or actual level of development determined by independent problem-solving and the learner's emerging or potential level of development. That is, it is the set of knowledge that the learner has the ability to learn currently but does not yet understand -- things that are "just out of reach". ZPD has also been expressed as the area in which students are challenged to learn, but learning is not too difficult nor too easy.