We undertook a self study to examine and develop our pedagogical content knowledge for teaching the nature of science. We explored two different uses of concept mapping to assess preservice teachers‟ ideas about the nature of science (NOS) in an elementary science methods course. The class was divided into two groups. Group 1 was provided with aspects of NOS as starter concepts for their maps, while Group 2 was asked to develop their own concepts related to “science”. We found that being given the NOS aspects constrained Group 1‟s ability to expand the connection of the main concept with other related words. On the other hand, Group 2 had difficulty moving beyond brainstorming related concepts. Based on this, we suggest that these two methods for concept mapping can be best used for different assessment purposes and at different points in NOS instruction.