A wiki is essentially a collaborative website. Wikis can be private in-house sites meant to serve a limited number of editors, or wide-open public sites where almost anyone can contribute. The most famous example of a public wiki is Wikipedia, an online encyclopedia whose articles are edited by volunteers and whose content is subject to change by nearly anyone. Wikipedia is one of the most popular reference sites on the Web, with around 60 million hits per day. Many history teachers are using wikis to build collaborative lessons, study guides, and activities.

Why Wiki?

Wikis are a pretty exciting technology for classroom teachers:

Students, teachers, and even parents could collaborate to gather, edit, and present information on a wiki.
A wiki could be used to build a classroom dictionary of terms in a subject area. For example, students could build a list of vocabulary or literary definitions for a course.
Students could also use a wiki as a class notes page that serves as a study guide for tests. Each student could contribute a set of notes and add comments to existing notes.
Another idea is to break kids up into small groups for a project or activity and have them paste their work on a wiki. One could then invite other student groups to comment.
Wikis could also be used to enhance professional collaboration. For example, teachers in a department or district could build a curriculum unit together or simply post their lessons and assignments.
A teacher could post words for students to expand into definitions.
Students could research new topics and contribute their findings
A wiki could be used as a portfolio showing development of a project
Teachers could develop and edit curriculae

EdTechTeacher "Collaboration with a Wiki" Tutorial

Wikis in Education Resources

Blogs, Wikis, Podcasts, and Other Powerful Web Tools for Classrooms (Paperback), by Will Richardson
Available on Amazon.com

Wide Open Spaces: Wikis, Ready or Not, by Brian Lamb
Review on EDUCAUSE

"Wikis in the Classroom", by Joyce Valenza
Article available on her blog

Warlick's Wiki
Information available on David Warlick's wiki site

Wikipedia
The world's most comprehensive encyclopedia. Unlike a print encyclopedia it is never "finished" as articles continue to evolve.

Wiktionary
Wiktionary is "a collaborative project to produce a free multilingual dictionary in every language, with definitions, etymologies, pronunciations and quotations."

Wikiquote
Wikiquote is "a free online compendium of quotations in every language, including sources (where known), translations of non-English quotes, and links to Wikipedia (http://en.wikipedia.org/) for further information."

Collaborative Commons Wiki
A wiki by independent school educators with the hope that educators will use this Commons to develop an understanding of The Read/Write Web, and in doing so make connections for collaboration, be it discussion or planning of joint projects. The wiki platform is from editme.com.

Three Popular Wiki Platforms

Wikispaces for Teachers
This popular wiki platform with educators offers no-cost and ad-free wikis for educators who subscribe to its educator program. Wikispaces will also help you add students as members of your wiki. Watch EdTechTeacher's four-part video tutorial on collaborative learning with Wikispaces to get started.

Wikis and Collaborative Learning: Wikispaces Part 1

Wikis and Collaborative Learning: Wikispaces Part 2

Wikis and Collaborative Learning: Wikispaces Part 3

Wikis and Collaborative Learning: Wikispaces Part 4

Pbworks for teachers
Formerly called Pbwiki, Pbworks is another popular wiki platform with free wikis for educators and an educator outreach program. EdTechTeacher's Justin Reich is currently leading an extensive research project evaluating Pbworks integration into K-12 classrooms.

Wetpaint for Teachers
Another popular wiki platform with with educators, it boasts a graphic-laden design that is popular with MS and Elementary school teachers.

A Wiki or Google Sites?

An increasingly popular alternative to a wiki is Google Sites. Formerly known as Google Pages, Google Sites is a free website creation tool that has incorporated features commonly associated with wikis. For instance, Google Sites includes a "revision history" of edits and provides the ability to insert comments. A significant Google Sites advantage is that multiple people can edit a web page at exactly the same time. Multiple people can edit a wiki page, but not at the exact same time. Google Sites is also intuitive and arguably less "clunky" than a wiki. That said, Google Sites is not a true wiki editor and lacks some of wiki features and flexibility.