This paper focuses particularly on the role of municipal science consultants in developing and maintaining network activities and connections among primary school science teachers. The hypothesis is that consultants play a crucial role in supporting strategic planning, and sustaining contacts and activities within professional learning networks. The research is framed by a project that involved 80 primary science teachers in 20 schools. The aim of the project was to develop network activities that facilitate sustainable change of the participating schools' collective culture and practice of science teaching. The authors were involved as researchers and evaluators in the project. Data consist of reports from the consultants about their participation in various network activities, school assessment reports and a longitudinal survey. Three distinct cases are analysed through the use of a framework of professional learning networks to assess the consultants' opportunities and constraints in terms of participating in network development. The results indicate that the consultants' roles in successful network formation is characterized by personal stable contacts within the science teacher community in the municipality, availability of municipal resources to support network activities, participation in strategic planning of municipal network support, and facilitation of the development of new teaching activities within schools or in collaboration between schools. These four distinctive features of municipal science consultants' participation in supporting network activities enable the participants to share and develop teaching activities.