www.ClassBlogmeister.com plug. The first classroom blogging engine--he built it in 2004 so that teachers could oversee the content. There are others now--to be honest, he would urge people to go to the others, because ClassBlogmeister was needed at the time but he hasn't really been able to keep it as current as he might like. He has 63,000 users on his service, which is free.
Wouldn't everyone concerned have been happier (including David) if he had released the code for ClassBlogmeister as free software three years ago? He's not making any money off it anyhow. He would probably have a few people helping him to keep it up to date and making improvements and fixes. He'd probably have more overall users but be responsible for hosting fewer of them himself. The only real drawback would be in taking some extra time to make it reasonably easy to install and set up for other people, but that's an up front investment that can pay off in the long run.