I have decided to apply AT to student blogs. For the first time next semester, I will ask students to keep their own blogs rather than contribute to a class blog. I will also keep a blog, à la Jo Iacovides - I will summarise and comment on what is happening on students' blogs. Thanks for that idea, Jo and H809!
I predict that I will find serious contradictions in the various relationships between the components of the activity system, which will account for why (some) students don't use their blogs or 'hate' blogging (read 'hate homework' and 'hate expectation'). I think this sort of overall evaluation will enable me to make a decision as to whether it is really worthwhile to continue to try to integrate blogging into my particular educational context. If I do have to abandon it, I reckon it will be time to change jobs, as I wish to work in a university where the system encourages and the students value formative learning opportunities. Trying to take a social constructivist approach in an exam-based culture is like trying to walk across a ceiling.