Alisa pointed out 
Tom Hoffman's blog last night. He appears to develop primarily using zope. Interesting stuff. I've added his blog to StuffSteveReads. He's been thinking in a wiki about developing a blogging system optimized for K-12 education. I tried editing the wiki, got an error, so I just forwarded him the comments in an email. His system was focused on mediating students and instructors and I suggested looking a bit more at group issues
One issue you might want to consider is enabling groups and peer review. You could have students be able to mark documents as "out for review". Reviewers could either add comments or make changes. The original author could receive a view that highlighted the comments and changes made by the reviewer. It might be useful to make the reviewing system anonymous for the author (but not the teacher). If I were using such a system, though, I would also want to be able to create group documents. The biggest problem I see with the system is the complexity of managing the public/private information. The private isn't really private: it will get revealed accidently sometimes (because someone's password will get exposed or they'll mark something for public viewing by mistake). My approach is to just use a wiki and make it clear from the beginning that everything you post will be public. If you want to do private writing, you do it privately and write it in a text editor, save it locally, and don't publish it on the server.
I spent a while this morning getting caught up on truthout.org. We're going to war with Iran, while we're losing the 'peace' with iraq and covering up global warming. Depressing.
On June 12th, Howard Dean's campaign posted a note encouraging folks to sign up with moveon. Since then, I've received a couple of notes from moveon to tell me that Dean, and later, Kerry "want my support". Today I got an email from Kerry's compaign -- I sent him an email once about a legislative issue and have received email from his office ever since. This email asked me to register for the Moveon Primary and provided the URL: http://www.moveon.org/pac/reg/ If you looked at the source of the html mail, however, clicking on the link would actually take you to this URL: http://www.johnkerry.com/site/R?i=nzXbdzfU0cv-V-V1i-CzVQ.. I understand their reasons -- they want to know how many people are clicking and who they are -- but I find the practice deceptive. If you put a URL in email, don't have a different URL underneath -- that's just wrong. It's just another reason why HTML mail is bad.