Awhile ago, Google pointed to some internal research in which it took roughly 90 seconds longer to find an email than to search for it. Users that took the find approach spent a considerable amount of time looking through their folders, sub folders etc. This was not only more inefficient than searching, but there was considerable time spent on the front end with folder organization.
I am not necessarily anti-folder or anti-label, but do hold in the Gmail ecosystem their logic comes from search. A label is only as good as the search behind it. With the limited amount of time teachers have it is better spent honing in on their search skills, than treating labels like folders.
In the slideshow that follows, I use animated Gifs (SnagIt) to demonstrate archiving, searching by author, keyword, author+keyword, and Advanced Search.