This research aims at analyzing the features of interactive dynamics in second graders' peer interactions (age 7-8) during cooperative writing in classroom settings. Focused on in-depth qualitative analyses of videotaped data, four pupil pairs' interactions have been examined in light of three dimensions: social, cooperative and cognitive. Within two main types of dynamics (favoring vs. not favoring learning), conjectures have been drawn about co-regulation processes in peer learning. While negative dynamics have shown to be detrimental for the cognitive processing of the task, thus needing teacher contextual regulation, positive dynamics have revealed three forms of teamwork, labelled self-reliant, autonomous and dependent. The results show that young learners, even when engaged in positive dynamics, are not always able to co-regulate peer learning. These findings call for teacher's careful observation in order to scaffold learners' cognitive processing.