Religious education in Baden-Württemberg is a regular subject at all public schools. Every pupil who visits a public school in Baden-Württemberg is in principle obliged to participate in the religious instruction of his confession.
Religious education, separated according to confessions, is given and supervised by commissioned representatives in accordance with the teachings and principles of the particular religious community. For a religious minority of at least eight pupils religious education has to be established at a school (§ 96 Education Act Baden-Württemberg).
Parents decide on their children's participation in religious education. After reaching the age of 14, the pupils themselves decide to participate. The signing out of religious instruction at the beginning of a school year must be submitted in writing to the school principal (§ 100 Education Act Baden-Württemberg). Pupils who do not attend religious education have to attend ethics as mandatory subject.
https://www.service-bw.de/leistung/-/sbw/Religionsunterricht++Abmeldung+erklaeren-943-leistung-0