The graph below identifies how wikis are used. (As you can see, encyclopedias are but a small segment of wiki use.)

blogs.atlassian.com/.../03/how_do_you_use.html
According to the website, "managing classroom information" fell into the "other" category. Hopefully, since this poll was compiled back in March, 2008, classroom use has expanded. In teaching practice, wikis can be used as collaborative spaces for student group assignments, teacher sharing spaces, class or school posting areas, student portfolios, etc.