Vygotsky's 'Zone of Proximal Development' refers to:

Vygotsky's socio-cultural theory distinguishes two developmental levels: the actual developmental level (what a learner can accomplish independently, unaided) and the potential developmental level (what the same learner can accomplish under adult guidance or in collaboration with a more capable peer). The Zone of Proximal Development (ZPD) is defined as the gap between these two levels — the range of tasks a learner cannot yet do alone but can do successfully with appropriate support (scaffolding) from a more knowledgeable person.

Applying this definition here: the correct description of the ZPD is the set of tasks the child can perform only with the guidance of a more knowledgeable person (a teacher, parent, or more capable peer) — exactly the guided band between independent performance and current inability.

• What the child can do independently describes the actual developmental level, not the ZPD — it is the starting point the zone is measured from, not the zone itself.

• What the child can't do independently is too broad: it includes both tasks reachable with guidance and tasks beyond reach altogether, so it fails to isolate a single developmental zone.

• What the child can do with guidance of a knowledgeable person precisely matches the ZPD — the tasks achievable through scaffolded support but not yet achievable alone.

• What the child can't do even under guidance of a knowledgeable person lies beyond the ZPD entirely — these tasks exceed the child's current potential developmental level.

Hence, Vygotsky's Zone of Proximal Development refers to what the child can do with the guidance of a knowledgeable person.