The investigators sought to design an instructional unit to enhance an understanding of the nature of science (NOS) by taking into account both instructional best practices and suggestions made by noted science philosopher Thomas Kuhn. Preservice secondary science teachers enrolled in a course, "Laboratory Techniques in the Teaching of Science," served as participants in action research. Sources of data used to inform instructional decisions included students' written reaction papers to the assigned readings, transcribed verbal comments made during class discussions and other in-class activities, and final reflection essays. Three iterative implementations of the instructional unit were attempted. The objectives of the study were essentially met. The instructional unit was able to provoke preservice teachers into wrestling with many substantive issues associated with the NOS. Implications concerning the design of explicit reflective NOS instruction are included.