I think that the idea of a central weblog exchange is wonderful. I’m sure that this would work with many classes, but many in US K-12 would likely point out that their schools have restrictions against publishing public pages. This is tough to get around. Either you have the teacher act as mediator, or you password protect the blog. Either of these would make an exchange possible, if a little difficult. Maybe a blog exchange could act as a “key master” for these blogs? This would alleviate the need for exchanging and managing passwords. Maybe set up like a social networking site. Teachers could make “friends” with other teachers. These “friends” could then access class blogs. Just some ideas.