An additional lesson which takes place only once can be created in the scheduling dialogue by the means of a special duty window or by an entry in the details window (see chapter. "Special duty"). However, you can also add already existing lessons.
How to add a teacher from a class' point of view
Set the scheduling dialogue to "Class". Now you can add another coupling line in the details window.
How to add a class from the teacher's point of view
If you want to add a class to a lesson, you simply do the same as above. Set the scheduling dialogue to "Teacher", and enter in the "Class" field the additional class, separating it by a comma.
Warning: Elements cannot be modified
If you set the scheduling dialogue to "Class", you cannot modify the entry in the "Class" field. However, you can switch to the teacher's view. The same applies for teachers.
If you set the scheduling dialogue to "Class", you cannot modify the entry in the "Class" field. However, you can switch to the teacher's view. The same applies for teachers.