I am designing a site for a school and I have reached a problem: I am putting teachers' websites (where the teachers post homework) under folders by the class they teach. However, some classes are taught by only one teacher. I find the idea of making a folder with only one option unnecessary, but having teachers' websites just in the parent folder (Teacher Websites) seems messy and confusing. What would you suggest?
If you find the major use case is that most teachers have multiple classes, then it makes sense to limit it by folder like you said. Sure, you may have some extraneous folders or folders with only one file in it, but it makes actually sorting through folders (aka teachers) easier, even if it does add a step to open the folder.
Remember, if you're saving the user time by adding a step, you're still increasing the efficiency and removing any questions or doubt. I'm not entirely clear on the situation, but it sounds like removing folders for specific teachers with only one class will actually make it more difficult for some students to find those teachers because some will have folders and others won't, and they may not know off-hand which do or don't.
Over time those students (or anyone searching) will wonder why it's slower, but even then the system will work over time better this way. Each year some teachers will pick up classes while others will drop some. With the foldered system in place there's no need to make any changes to the layout, only to update the content within the folders. Meaning no teaching students again how to sort and no mess on each new semester.