The purpose of the school classes file is to be able to identify old class photos (which are encoded in old photos and generally not in postcards, unless it is an edited postcard).
This makes it possible to identify the localities, schools and classes which are generally without indication.
Old class photos often have a blackboard with the name and year of the class. After 1918 it seems that this habit disappeared.
A teacher will have about forty active classes and a college several hundred.
By identifying only one of these classes it is enough to identify the other old class photos