MEChS is one of five projects grown out of the scientific MILES (Methodological Issues in Longitudinal Educational Studies) -consortium, which is coordinated by the Leibniz Institute for Science and Mathematics Education (IPN) at Kiel. In this co-operative project data from two longitudinal studies LAU (Aspects of learning background and learning development) and KESS (Competencies and attitudes of students), which have been conducted during the 1990s and the 2000s in Hamburg, was reanalyzed with the aim of answering methodological and substantial questions of longitudinal research in depth.