Self-directed learning (SDL) is not a new educational principle. It was influenced by the ideas of the American progressive education and the European educational reform movement (1890-1933).During and after WWII, educators re-implemented the authoritarian and teacher-centred methods of the mid 19th century. But due to the political circumstances, the general shift from teacher-centred to learner-centred methodology and the publications of Cyril Houle and Allen Tough in the 1960s and 1970s, SDL gained momentum again.In general, the terms ?SDL?, ?open education? and ?Offener Unterricht? in German, which is used as an umbrella term for all non-traditional methods and ideas, denote the active involvement of learners and the responsibility for their own learning processes. Because of these areas of overlap, researchers failed to define each of the terms in a generally acceptable way. Subsequently, the ambitions of educators shifted from defining to explaining SDL in various stage models. In this thesis, the most popular models have been singled out for explanation, which are Ramseger?s indicator concept, Brügelmann?s dimension model and Peschel?s ?Stufen der Öffnung von Unterricht?. These stage models do not only show how open education methods can be implemented in classes but also provide the rationales that underlie them. Three of them are explained and critically analysed, which are the issue of heterogeneity in classes (learning styles and learning strategies), the constructivist school of thought and Deci and Ryan?s ?Self-Determination Theory?.In addition, the thesis deals with the different variations of assessing students? performances in open education classes. Since secondary schools and elementary and alternative schools differ in their organisations, structures and curricula, the various types of assessments are analysed separately. Furthermore, the thesis shows how open education methods are successfully used in Styrian schools.