There are different regulations in each state as to when compulsory school attendance ends or when a pupil can be released prematurely from compulsory education upon application by the school board. Some federal states (Bremen, Hamburg, Sachsen, Rheinland-Pfalz and Sachsen-Anhalt) have a uniform compulsory education with a duration of twelve years. It's eleven years in Hamburg. During this time, students must attend a full-time school. After nine years (ten years in Bremen) compulsory education can also be fulfilled by attending a part-time school (vocational school).
You will find important information concerning the school leaving conditions at: https://www.ihk-trier.de/ihk-trier/Integrale?MODULE=Frontend.Media&ACTION=ViewMediaObject&Media.PK=4457&Media.Object.ObjectType=full