In a science education methods course, groups of students were initially involved in a face-to-face discussion and were sensitized about certain conflicting claims regarding a puzzling observation or set of observations. They were then instructed to resolve their conflicting ideas through electronic discussion. Students had two weeks time to participate in the online discussion by posting their points of view as well as replying to others' postings using the asynchronous discussion feature of WebCT. Students discussed these claims, and conducted more experiments, whenever they felt they need, in order to reach consensus about their opposing claims. The online discussion was anonymous in order to encourage students' participation in dialogue and negotiation of meaning. It was thus possible to identify students' alternative frameworks and attempt to facilitate conceptual change and understanding. The instructor of the course participated in the online discussion as a student by asking challenging questions. Students were supposed after participating in the online discussion to reach consensus and individually email their answers to the instructor. The data analysis provided ample evidence of students' patterns of thinking and their difficulties to be involved in evidence-based argumentation and reach valid conclusions acting as "practicing scientists" by forming and testing relevant hypotheses. (Contains 3 tables.)