This study examined the outcomes of a unit that integrates explicit teaching of general reasoning patterns into the teaching of a specific science content. Specifically, this article examined the teaching of argumentation skills in the context of dilemmas in human genetics. Before instruction only a minority (16.2%) of the students referred to correct, specific biological knowledge in constructing arguments in the context of dilemmas in genetics. Approximately 90% of the students were successful in formulating simple arguments. An assessment that took place following instruction supported the conclusion that integrating explicit teaching of argumentation into the teaching of dilemmas in human genetics enhances performance in both biological knowledge and argumentation. An increase was found in the frequency of students who referred to correct, specific biological knowledge in constructing arguments. Students in the experimental group scored significantly higher than students in the comparison group in a test of genetics knowledge. An increase was also found in the quality of students' argumentation. Students were able to transfer the reasoning abilities taught in the context of genetics to the context of dilemmas taken from everyday life. The effects of metacognitive thinking and of changing students' thinking dispositions by modifying what is considered valuable in the class culture are discussed. © 2002 John Wiley & Sons, Inc. J Res Sci Teach 39: 35–62, 2002