Vygotsky, L.S. (19332-34/1997). 'The zone of proximal development, often abbreviated as ZPD (zona blizhaishego razvitiia, in original Russian), is best understood as the zone of the closest, most immediate psychological development of the children that includes a wide range of their emotional, cognitive, and volitional psychological processes. The Problem of Age. in The Collected Works of L. S. Vygotsky, Volume 5, 1998, pp. 187-205
