Firstly I checked with a member of senior management whether it would be OK. He said that I should teach the students not to use their full names, not to post images that included their faces, and to make sure comments didn't reveal where students would be at a future time. All of these rules seem to make a lot of sense to me.
I started a edublogs.org blog. There is advice on their page on how to set up the blog and educate the students how to use it. I have taken their advice and I only allow students to comment on the posts that I make. So far. After the students have learned to contribute quality comments they are allowed to write their own posts. Then it is possible to allow students to have their own blog, which is something I am not keen on.
I am still at the point where I write the blog posts and the students comment. The class seem to enjoy this, but I am struggling to get them to do more than write very simple comments and they don't respond to each other. I wonder if my issue is that I am not giving them enough time to complete the work. However, even groups who finish first don't automatically read and reply to others. I would like to see this happen.
It goes back to the classic issue of getting students to look back over their own work and act on the comments that the teacher makes. I have always struggled with this when we seem to move through topics and themes at a high rate, particularly when you might have one 2.5 hour per week.
I am pleased that I am managing to consistently use the blog with the students, once per week for half an hour.
My Year 9 blog can be found at http://missrogerson.edublogs.org