The main characteristics of the developmentof the educational system are processes of ifferentiation and integration. An even greater numer of pidagogical fields of work and institutions become part of the educational system. Based on the example of primary school and kindergarden, the authors argue that both organisztions are in the middle of different phases of this process of modernization which proceeds at a different pace, respectively. The system- and modermization-theoretical perspecitveadopted in this contribution paints a more precise picture of the field of tension between historically grown differences and present-day demands regarding the connectivity of these two organisztions. The study's aim is to develop a comprehensive theory of structural integration processes.