If you cannot see the parent and class groups, you have to make yourself a class teacher or a co-class teacher of the corresponding class. Only once you have made this selection you will be synchronised in the corresponding parent group.
Open the settings via the drop-down menu in the header at the top right, select the top tile with "Change my profile, school data & passwords" and scroll down to the very bottom.
IMPORTANT: In order to be able to register as a class teacher or co-class teacher, you first have to choose your code in Sdui. first choose your initials in Sdui. Otherwise you will not see this option.
In Sdui there can only be one class teacher per class. However, several co-class teachers can be added to a class.