Understanding education systems as a whole is an important prerequisite for working in the fields of education, upbringing, and pedagogy. The introduction to the theory of schools prepares the social science foundations necessary to comprehend education systems, their functions, and interconnections. By referring to the description of the education system as a social reality in terms of function and structure, the expanded school theory is presented comprehensively and understandably. Through empirical description, Helmut Fend provides students of educational science with a practice-oriented understanding of the processes and offers suggestions for the future design of institutionalized teaching and learning.