This study explores the processes of collaborative teacher learning in a Lesson Study group at a lower secondary school in Norway. In this context, teacher learning is understood from a sociocultural perspective, as making sense of the world, solving problems and exploring new perspectives through social interaction. Audio-recorded teacher discussions are analysed, using a coding system adapted to identify whether teachers' reports of observations from the classroom are related to interpretation, evaluation and further planning. Findings reveal a strong link between reported and interpreted observations, evaluation of student learning and teaching, and further planning. The article suggests that the sharing phase of the post-research lesson discussions provided the foundation for this relationship. Planned observations operationalised through observation forms contributed to rich reports of observations from several observers. The collaborative sharing process opened up for extended perspectives on the research lessons. However, the most crucial aspect for teacher learning was shared ownership of challenges and a common wish to change and improve the next lesson. These findings contribute to enlighten the potential of teacher learning processes in Lesson Study.