"The entire school system shall be under the supervision of the state.-- Parents and guardians shall have the right to decide whether children shall receive religious instruction."
According to article 7, the state oversees and regulate the schools. Private schools must also adhere to these regulations. According to the German federal system, the governments of each state determine specific school regulations at the local level. That is why the school systems in individual federal states differ to some extents.
Article 7 also asserts that no child has to attend religion classes. Parents can decide whether their child takes part in religious courses at school. Same applies to the teachers- teachers cannot be obliged to teach religion as a school subject.