A WikiWikiWeb allows its users to quickly and easily add or modify pages. Its best use is for collecting information on a very specific subject to build a powerful knowledge base. But without contributors or editorial staff it won't be a very useful tool.
Running a site where anybody can change anything brings risks. While many contributors add useful notes and information, there can also be black sheep who annoy others or delete content in an attempt to bring some fun to their lives. Even if it is rather easy to bring back lost content due to the unremovable version history, this can be a lot of effort because of the amount of free time 5th grade pupils usually have.
Therefore you should know how to prevail people upon to play nicely. Restricting a wiki with some sort of authentication mechanism, which requires users to register before they're allowed to do anything, would really hurt the whole concept; you should then instead try PhpNuke or similar portal software.