In Lower Saxony, a decree of 20 December 2019 requires every school to develop a Vertretungskonzept, a substitution concept, to avoid lost lessons as far as possible. Lessons that cannot be avoided must not be lost one-sidedly at the expense of particular classes or subjects. A school in Dortmund sets an order for absences of medium length. First comes a teacher of the same subject, then a teacher of the same class, and only then general cover. Its teachers are told to check the Vertretungsplan, the substitution plan, several times a day, for example through push messages from the school’s app.