They can
- provide information ( be it text, images, video, podcasts)
- create a space for discussion and sharing ideas
- encourage collaboration
- display students' work etc
I am keen to set up a wiki using Wiki spaces but see two challenges. Firstly, keeping the site current and adding to it regularly to keep it active and "alive' and secondly, encouraging and enthusing others to make a contribution to the site.
The school library where I work would be ideal for creating a wiki. On it I could put info about opening times, borrowing policy, procedures etc. Advertising and promoting Book Week short-listed books, authors and illustrators, Literature Circles and a place for sharing photos, upcoming events, news etc could all be placed on a wiki.
Each class could also create their own wiki and do things like debating, pick-a-path stories, solving open-ended math questions, orientation of new students (what you need to know) to name a few.