Oftentimes people point to research conducted in a university context to ask why teachers aren't implementing social media services into their teaching practice. The simple answer is schools are different to universities, our clientele is different. The clientele of a university is it's students - the clientele of a school is society in general and parents in particular. Before we try and convince teachers to grasp change in education, it is always necessary to convince parents that it is safe to do so.
I wonder what parents' first reaction would be if they knew that their child had 2000 people reading their child's blog. From my experience as a teacher there could well be a reaction of fear. The idea that 2000 strangers were watching their child would frighten some parents, especially parents who are unaware of blogs and their uses. I think this is part of the reason why we are slow to adopt new technologies in schools. Here is one principal's recent reaction to Facebook. The comments about the article speaks loudest of all about why social media is not being used in schools.
Ten years ago I was teaching students how to use email using Hotmail. Within a very short time Hotmail and other web based email was blocked by the school system I work in, and it took a number of years before an email service was provided to each student. Why was email blocked and then released under strict control? Because of the fear of students sending inappropriate messages to each other. YouTube is blocked. Why? Same reason, only its video not messages.
No doubt, in a few years time all manner of social media services will be available to students under strict, filtered conditions. In the meantime teachers will be unable to fully implement Personal Learning Networks for their students.