Based on the learning-to-notice framework according to Van Es and Sherin (2021), the study examines the key aspects of noticing of preservice primary school teachers in mathematics. For this purpose, a university course was developed as a study environment. Preservice teachers videorecorded their self-designed lessons with primary school children. Together with peers they reflected on their teaching observed in the video vignette through a group interview. Fifteen interviews were conducted. Data was analyzed using Grounded Theory methods (Corbin & Strauss, 2015). The results show that preservice teachers gained insights through the reflection process about various facets of children’s learning processes and their own teaching activities. During the group interview they connected those facets and interpreted them in depth.