Natural science in education can be summarized as a complex system. The professional and methodological task in the teaching of natural sciences is to convey this complexity. The terms and models of graph theory can be used to model the system approach, such as networks. Networks consist of elements and connections between them, which can be well represented by graphs. Growing networks have a scale-independent property, i.e. the rich get richer principle applies. Internal connections may also appear within the networks, which strengthen the network. New theories related to education appeared at the turn of the 19th and 20th centuries and are called reform or progressive pedagogical methods. Their common basic ideas include children's freedom, getting to know and helping the child as an individual, the coordinating and helping role of the teacher, and the existence of the appropriate quality of the pedagogical environment.