In a European project about formative assessment, Local Working Groups (LWGs) from six participating countries made use of a format for teacher-researcher collaboration. The activities in each LWG involved discussions and reflections about implementation of four assessment formats. A key aim was close collaboration between teachers and researchers to develop teachers' formative assessment practices, which were partially evidenced with changes in attributes of self-efficacy. The research question was: to what extent do working with formative assessment strategies in collaboration with researchers and other teachers differentially affect individual self-efficacy beliefs of practicing teachers across different educational contexts? A 12-item teacher questionnaire, with items selected from a commonly used international instrument for science teaching self-efficacy, was distributed to the participating teachers before and after their work in the LWGs. A novel method of analysis using networks where participants from different LWGs were linked based on the similarities of their answers, revealed differences between empirically identified groups and larger super groups of participants. These analyses showed, for example, that one group of teachers perceived themselves to have knowledge about using formative assessment but did not have the skills to use it effectively. It is suggested that future research and development projects may use this new methodology to pinpoint groups, which seem to respond differently to interventions and modify guidance or instruction accordingly.