The purpose of the reported research was to build understanding of science teacher educators' (STEs') development of pedagogical knowledge (PK) using critical experiences (CEs). It further investigated the role of CEs in developing PK for STEs, the ways that STEs' notions of PK develop and change over their careers, and the dispositions necessary to developing an understanding of PK for science teacher education. Eight STEs from six Australian universities identified CEs from their careers during an interview (all worked as secondary school science teachers before becoming STEs). Interview transcripts were combined with notes from participants to form cases, which were analyzed to identify categories of CEs and themes for each participant. Morine-Dershimer and Kent's 1999 model of PK was used to help explain shifts and changes in thinking and teaching practice that participants' CEs revealed. The research indicates that individual themes are important and that dispositions help to identify participants' beliefs and attitudes that are in operation to assist with developing PK.