Over 99% of Germans age 15 and above are estimated to be able to read and write. However, a growing number of inhabitants are functionally illiterate. Responsibility for educational oversight in Germany lies primarily with the individual federated states. Since the 1960s, a reform movement attempted to unify secondary education in a Gesamtschule (comprehensive school); several West German states later simplified their school system to two or three tiers. A system of apprenticeship called Duale Ausbildung ("dual education") allows pupils in vocational training to learn in a company as well as in a state-run vocational school.
Optional kindergarten education is provided for all children between three and six years old, after which school attendance is compulsory for at least nine years. Primary education usually lasts for four years and public schools are not stratified at this stage. In contrast, secondary education includes three traditional types of schools focused on different levels of academic ability: the Gymnasium enrols the most gifted children and prepares students for university studies; the Realschule for intermediate students lasts six years; the Hauptschule prepares pupils for vocational education.
The general entrance requirement for university is Abitur, a qualification normally based on continuous assessment during the last few years at school and final examinations; however there are a number of exceptions, and precise requirements vary, depending on the state, the university and the subject. Germany's universities are recognised internationally; in the Academic Ranking of World Universities (ARWU) for 2008, six of the top 100 universities in the world are in Germany, and 18 of the top 200. Nearly all German universities are public institutions, charging tuition fees of €50–500 per semester for each student