When Vygotsky Suggested That Development Takes Place Within a "Zone

When Vygotsky suggested that development takes place within a "zone of proximal development", he meant that

A) a child's problem solving depends on the social context within which it occurs.
B) children never seem to work up to their actual ability levels.
C) development occurs in clearly-defined stages.
D) children accomplish more when working alone than when working in groups.
E) teachers should set aside quiet places in their classrooms so that children will not be disturbed when working.