This article focuses on the development of professional learning communities (PLCs), which are communities within schools, composed of voluntary participating teachers facilitated by school principals with a specific task to accomplish as part of a larger innovation project. Four PLCs were observed during 3 years by using questionnaires and participatory research. The questionnaires revealed that PLCs differed in their group characteristics, collective learning processes and outcomes. Through participatory research, we explored seven elements affecting the development of PLCs, namely, task perceptions, group composition, tensions between roles, beliefs about alignment, reflective dialogues, socialisation and ownership. Beliefs about alignment, ownership and socialisation had sufficient impact on the development of the PLCs. A case study including two contrasting PLCs indicated interrelations between task perceptions and ownership by members and between ownership and socialisation activities. Regarding implications, this research suggests to explicitly create and facilitate reflective dialogues and ownership over time for PLCs to flourish.