This article examines the potential of mobile computing and Web 2.0 technology to support knowledge building in formal and informal settings. Desktop-based knowledge building tools have limited affordances of supporting one-to-one access, learning "in situ," and seamless integration in and out of school environments. In this initial study, we explore how recent advances of mobile and Web 2.0 technologies can be utilized to support seamless knowledge building processes and to enhance contextualized learning experiences across multiple locations. Using design research as a methodological framework, we analyzed current practices and configurations of mobile learning in one primary school in Singapore, and codesigned a learning scenario with teachers toward seamless knowledge building experiences. The artifacts of primary grade 4 students created in the Google Maps space were analyzed to examine the knowledge building processes based on a location-based mobile learning scenario. We conclude by discussing both possibilities and challenges of knowledge building using mobile Web 2.0 technologies based on our early experiences. (Contains 1 figure and 2 tables.)