In recent years, the emphasis on interaction in data use has grown because of its potential to support individual teachers. However, in practice, teachers do not appear to interact widely in their use of data, either formally or informally. To gain knowledge of how sustainable data use interactions can be facilitated, this study investigated how formal data use in teams of teachers affects the teachers' informal interactive data use. A survey provided insight into 72 teachers' perceptions of data use discussion, interpretation, diagnosis and action at formal team meetings. Subsequently, social network analysis of seven teacher informal data use networks revealed that teachers with more positive perceptions about formal data use become more active in their informal data use network. Within the problem diagnosis phase, this tendency is to generalize across the participating teams. The results of this study imply that, particularly to define problems and formulate actions based on pupil learning outcome data, it is necessary to ensure strong connections between teachers in formal groupings in order to affect their informal interactive behaviour.