This study describes the characteristics of pre-service teachers' discourse on a WebCT Bulletin Board in their investigations of local streams in an integrated mathematics and science course. A qualitative analysis of data revealed that the pre-service teachers conducted collaborative discourse in framing their research questions, conducting research and writing reports. The science teacher educator provided feedback and carefully crafted prompts to help pre-service teachers develop and refine their work. Overall, the online discourse formats enhance out-of-class communication and support collaborative group work. But the discourse on the critical examination of one another's point of views rooted in scientific inquiry appeared to be missing. It is suggested that pre-service teachers should be given more guidance and opportunities in science courses in carrying out scientific discourse that reflects reform-based scientific inquiry.