“…van Geert's modeling of Vygotsky's ZPD grows out of his previous efforts of a similar kind [van Geert, 1992] and is solidly based on his long interest in formal analysis of theories that claim to study development [van Geert, 1983[van Geert, , 1986[van Geert, , 1987[van Geert, , 1988. In some sense, van Geert's focus on the ZPD is incidental -he is not interested in the whole complexity of that term [see Valsiner and van der Veer, 1993, for a substantive analysis], but rather in two spe cific features of the concept: (a) the emphasis on systemic (mutual) causality, and (b) a focus on the forward-oriented time-bound nature of development.…”