In this paper it is shown that the Soviet psychologist Vygotsky's well-known concept of the zone of proximal development arose in the practice of intelligence testing. More specifically, Vygotsky used the concept to explain the phenomenon of regression towards the mean of IQ scores. It is claimed that this way of thinking about the zone of proximal development contradicts its current Western interpretations. In addition, it is argued that Vygotsky's original interpretation had several unfortunate implications that conflicted with his own larger body of writings as well.