simply barring access not only potentially prevents students from experiencing the positive aspects of IM, but also fails to address the fact that most of them probably use it at home anyway. The very least the school could do would be to teach students how to remain safe in such environments.
IM, especially if there is a group or conference mode available, is a great way to have a discussion with people in other locations. Real businesses use IM to enable virtual teams to get together, or for teams to have a virtual meeting. Throw in a web cam facility and you have rudimentary video conferencing which can only enhance the students’ opportunities to participate in meaningful discussions as part of their work. You can find out more about keeping safe in forums and similar environments by going here.
Finally, it’s worth mentioning the opportunities collaborate on documents in real time. For example, look at Writely, at http://www.writely.com/, or some of the other facilities listed at http://www.shambles.net/web2/.
David Jakes looks at using Flickr and using wikis in the classroom at http://www.techlearning.com/blog/main/archives/2006/03/the changing fa.html.