This design-based research study looks at how a learning unit to support the development of a knowledge community activity was designed within Diigo, a social bookmarking tool. The Diigo learning unit was divided into five one-week lessons that aligned with course topics and provided numerous opportunities for students to interact and collaborate with each other using the various sharing and communication features of Diigo. This unit served two purposes: to facilitate learning on specific course topics and to support the development of lifelong learning skills. Through two iterations of design and implementation, this case study helps illuminate the points at which students needed additional scaffolding and motivational support in order to successfully engage in community-based knowledge activities. Specifically, students struggled to value and orient themselves toward the concept of collective knowledge in this computer-mediated context, and also found it difficult to connect the class group and activity to the types of professional development activities inservice teachers might engage in when teaching.