A learning community works with a collective knowledge space where members contribute and interact with one another's ideas to advance their community's knowledge. This study aims to explore designs of collective knowledge space to support cross-community interaction. A design experiment was conducted in four grade 5 classrooms with the support of Knowledge Forum over a school year. As students conducted focused inquiry and discourse within their own community, they reviewed productive threads of ideas and created "super notes" (idea thread syntheses) for cross-community sharing and interaction. A set of "super notes" from previous classrooms studying human body systems was also posted in the cross-community space. Qualitative analyses results showed that the students wrote and posted "super notes" to capture substantive idea progress and deepening questions that had emerged from their inquiry. Social network analysis of who had read whose "super notes" revealed extensive social interactions between the four classrooms as well as among the students within each classroom. Analysis of the classroom conversations that followed the "super notes" reading elaborated how students built on the insights gained from the cross-classroom interactions to develop deeper understandings in their home classroom. Analyses of teacher interviews and observation data documented the teachers' roles to contextualize the purpose of the cross-classroom space, support "super notes" reading and writing, and scaffold cross-classroom connection and conversation.