How to accept private homework files in groupsite?

I am looking to post homework publicly to our group and have members send their homework files to use privately. Sure, we could take the files by email, but though it would be nice if they could be posted in organized folders by homework assignment here on groupsite.

Is anyone using Groupsite as a vitual classroom who has a suggestion for how to do this?

The file manager can't handle this as all files in any publicly visible folder are also publicly visible.

Thanks!