A reconceptualization of the zone of proximal development (ZPD) is proposed by introducing the notion of dialogicality and voice. Drawing on Bakhtin's semiotics, it is argued that the dialogical interactions occurring within the ZPD must be understood in a larger context to go beyond the visible and audible participants. More specifically, in addition to the first voice of the more capable participant and the second voice of the less competent participant, there is a third voice that serves as an immediate agenda of the ZPD. The third voice exerts its influence through the first voice by mediating the latter's intrapsychological functioning. The compatibility between the agenda of the third voice and the developmental goals of the zone determines whether the progression through the ZPD is enhanced or constrained. Standardized testing is given as an example of the third voice with a focus on its compatibility with the developmental goal of the ZPD.