The purpose of this text is to explore how schools can become professional learning communities, involving teachers who continuously engage in building and sharing knowledge. We use theory and a model of knowledge conversion from the field of organizational learning to explore knowledge sharing within schools. The presented findings are based on a research project in a Norwegian secondary school. The data analysis discusses two circumstances of knowledge sharing, captured in the categories creation moments and bumpy moments. While knowledge sharing activities at team levels led to knowledge creation moments, whole staff assemblies proved to be challenging meeting places and bumpy moments occurred. We suggest that knowledge sharing as a key to developing professional learning communities needs to be organizationally supported.