We examined the integration of knowledge building community culture within a group of preschool teachers and its impact on their identities and practices. We traced how this group of preschool teachers came together as an online knowledge building community (KBC) and explored knowledge building (KB) practice during home-based learning caused by the COVID-19 lockdown. This KBC aimed to generate diverse ideas and encourage knowledge creation among community members. The study spanned three months during the lockdown period. Three aspects of the KB culture were expanded in this study: (a) idea improvement, (b) knowledge building discourse, and (c) collective and shared responsibility. We present the case studies of four teachers in the community, the transformation in their identities and practice derived from discussions in the KBC weekly meetings, interviews, and their posts on the Knowledge Forum (KF), an online discourse forum designed to support KB. Findings show trends in the transformation of teachers' identities and the way they thrived on diverse ideas from the community, alongside their openness towards novel ways of teaching practice and their willingness to approach and take on challenges. The potential and limitations of the KBC on community-based professional development are also discussed.