We describe two iterations of the design, development, implementation and evaluation of small online activity and reflection blogging groups into a large undergraduate lecture course in nutrition. Our goal was to promote student learning and conceptual change through reflection and interaction in blog conversations. We found the blog conversations to be highly useful to the instructors as a source of data on student understandings and misconceptions of course topics. These misconceptions could then be addressed with further instruction. We found that, even with initial training, graduate teaching assistants needed significant guidance in facilitation strategies and that finding the ideal balance between structure and autonomy is a design challenge.