Mathematics and science are closely linked not only as sciences, but also in teaching and learning at school. Despite this connection, transferring of the competencies developed in both subjects is not easy for students. In particular, lower secondary school students taking their first steps towards mathematization in physics need to learn how to use mathematical concepts and skills to work through physicstextendashmathematical problems and develop their understanding of physics. This includes both purely technical and formal skills, such as the skill of rearranging equations, as well as structural skills needed to link mathematical structures to physical models and concepts. Most importantly, they must learn semantic reasoning, which assigns physical meaning to mathematical symbols. In order to know students’ competencies, preferences and strategies in more detail, several studies were conducted. A preliminary interview study with 8th grade students analysed their attitudes towards the role of mathematics in physics and, in particular, the role of different representationstextemdashalgebraic expressions, graphs and verbal explanations. In a laboratory study, also with 8th grade students, a qualitative setting was used to analyse how they manage the transfer between these different forms of representations. Three forms of structural skills were observed: balancing mathematical and physical aspects, focussing on mathematics and focussing on physics. These skills are illustrated in this paper with examples from the study.