In this qualitative case study the authors explored secondary social studies preservice teachers’ abilities to discern the digitized primary resources available to them for historical thinking instruction. The results revealed that two themes emerged from the initial data analysis: First, the preservice teachers were able to identify and rationalize an importance of digitized primary source websites in teaching the social studies. Second, the pedagogical knowledge preservice teachers held regarding historical thinking was made apparent through their evaluation of the website’s historical thinking task. The authors used the teacher cognition scholarship of Shulman in order to suggest that the preservice teachers’ enumerated knowledge sources are vital in tracing teachers' decisions.