PCK change can be conceptualized in several ways. In the present section. I will distinguish different categories of this change, based on a constructivist view on cognitive development. According to this view, people make meaning for themselves: they learn through actively constructing knowledge. This process can be described in terms of Piaget(1972) as follows. A new experience might be assimilated by a person into his or her current cognitive structure. The experience might, however, be in conflict with the current cognitive structure, possibly resulting in a process of accommodation to the new information From the assimilation point of view, PCK change can be labeled as PCK extension. I will split up this category of PCK change in two sub categories: (i) development, and (ii) growth. From the accommodation point of view, PCK change can be labeled as PCK reconstruction. I will elaborate the categories concisely as follows (see also the scheme in Figure 4)