It is true that modern teaching is faced with heterogeneous students. Ironically, this is not a recent development: students have always been different. Consequently, there is a broad discourse on "heterogeneity" in education. On the normative level of meta-narratives about modern democracy one will find the idea that more and more people have to be included in the modern welfare state. Nevertheless, before talking about inclusion one has to deal with the mechanisms of exclusion, if one is interested in the phenomenon of heterogeneity. At the heart of it, one will find the debate on the meaning of differences between students from an age group and their implications for school-based learning. Even more basically, Didaktik has to give a response on the dilemma arising of balancing "individual" and "collective" modes of teaching. However, Didaktik theory speaks in the singular and in the light of normality. It normally speaks of generalized homogenized students, axis-constructions and vertexes in the singular, denying their heterogeneity. How can the teacher's relation to this simultaneous heterogeneity be carried out in a justified way? The central idea of the book is to explore whether this professional Didaktik challenge can be studied through the concept of the others' "strangeness". This volume analyzes the constructions of heterogeneity in pedagogy based on the leitmotif of the stranger. In doing so, the stranger is seen as a didactic key. The book shows that there is a necessity to understand the filter of strangeness/otherness. Beyond that it elaborates criteria for establishing the filter and didactically relevant mechanisms of this filter.