The contributions to the open access volume are comprehensive summaries of important research findings from the two comprehensive interdisciplinary longitudinal studies BiKS-3-18 and BiKS-8-18 conducted by the research unit "BiKS" (“Educational Processes, Development of Competencies, and Formation of Educational Decisions”) funded by the German Research Foundation. The aim of the book is to present selected important findings from these comprehensive longitudinal educational studies; in addition, the edition also aims to provide an overview of the design and measurements of the two surveys.