The purpose of this study is to develop a flow map for history of science instruction on nature of science (NOS) using a cognitive strategy. This is done to enhance overall scientific literacy through specificity and reflectiveness, and to examine pre-service elementary teachers' understanding of the NOS using NOS flow maps concerning Galileo's discovery of sunspots. There exists a general consensus in the science education literature regarding the goal of enhancing learners' views of the NOS. An extensive body of research in the field has highlighted the effectiveness of explicit NOS instructional approaches in improving learners' views on the NOS. Because it is valuable to introduce elementary students to some of the ideas developed by Kuhn, pre-service elementary teachers' understanding of the NOS was explored using an explicit NOS flow map developed as an instructional tool. The lessons combined cognitive conflict strategies in episodes concerning the history of science (Galileo's discovery of sunspots) with accompanying responses consisting of illustrations and questions. The lessons were designed to spend 50 minutes on study of the history of science, including conflict strategy, and 30 minutes on an explicit NOS flow map including all elements of the NOS. Students demonstrated understanding of tentativeness of scientific knowledge, and the lack of a universal scientific method. Therefore, instruction based on an NOS flow map is a promising method to enhance science teaching and learning.