Per-user private forums?

I'm a teacher, and I'm using Drupal to manage my course web site. I've been using it for a couple years now, and in general it has worked really well. There's just one feature that I really, really want and have so far not been able to set up practically: private forums for each student.

I've successfully used taxonomy_access to control who can see a section of the forums. For example, I've established roles called Fall2006, Spring2007, Fall2007, and soon Spring2008. Then I can assign students to those roles as they sign up, and set up permissions so that each class can access its own forums but no one else's. That's fine. But what I'd really like is to set up a private forum for each student. So in a class of twenty students, there would be twenty forums, one for each student; I would be able to access all of them, but individual students would only be able to access their own.

Theoretically, this is possible to set up using taxonomy_access. But I would have to set up a separate role for every single student, and assign permissions for every forum - I ran the numbers at one point and it works out to several thousand configuration changes to set up private forums for twenty students. I don't have that kind of time, and even if I did, chances are good that I would make mistakes in the configuration and wind up in permissions hell all term.

I've spent some time searching the forums here, and found many people who want private forums for moderators and such, but that's not quite the same thing. I am aware of DrupalEd, but I'm not sure whether it actually does what I want. DrupalEd.org is singularly uninformative about DrupalEd's capabilities and requirements. In fact, as far as I can tell there's no useful information of any kind at all on DrupalEd.org.

Anyway, for the moment I don't have the option even to upgrade to Drupal 5.x. The systems administrator is planning to upgrade next summer. Several other teachers depend heavily on flexinode stuff which we determined is probably going to get fubared when we upgrade to five or higher, and we can't deal with that kind of issue during term time. So for the moment I'm stuck with 4.7.

The sysadmin is happy to install extra modules on request. Is there any way I can do this given my technical constraints? Or am I stuck continuing as I have been?