There appears to be an almost universal commitment among science educators to promote the goal of student understanding of the nature of science. Recent disagreements among philosophers of science and between philosophers and other groups such as scientists and science educators about the nature of science, however, leave classroom teachers in a quandry: If experts disagree about the nature of science, how should we decide what to teach students? In this article, the authors first reconsider what level of understanding of the nature of science students should experience so that they can become both intelligent consumers of scientific information and effective local and global citizens. Second, based on an analysis of the literature, it appears that there is a general agreement among science education stakeholders regarding a set of descriptors that can be used to judge which questions or fields of study are more scientific or less scientific than others. Therefore, we propose that most precollege teachers should attempt to teach students how to use these descriptors to judge the relative merits of knowledge claims instead of teaching a set of rules that attempt to demarcate science completely from nonscience. Finally, we suggest two classroom activities based on this proposal and draw some implications for teacher preparation and future research. © 1999 John Wiley & Sons, Inc. Sci Ed83:493–509, 1999.