Vasily V. Davydov's solved the problem between situated and abstract knowledge and integrated these conceptions into a connected theory of knowledge and thinking. His use of germ-cell models as a methodological tool is the key to understand this integration of abstract knowledge with the concrete complex and situated knowledge of a domain. I will show how I built on these ideas in my research of children's learning and development by presenting a design experiment I conducted. The aim in this article is to illustrate the importance but also the complexity of using germ-cell models in developmental teaching as a tool focusing on the students' activity that orient children to formulate core models as their own tool to, reflect and analyse within the complexity of concrete life scenarios. The design experiment demonstrates that a primary-substantial abstraction may be a first step in formulating germ-cell models that can evolve so different subject areas can be connected when ascending to the concrete in developmental teaching. To accomplish this, it was important to take the children's perspective in the teaching process as a 'double move' between children's motive orientation and the subject matter area. The design experiment included the subject areas of biology, history and geography focusing on the evolution of animals, the origin of man and the historical change of societies.