These are just some examples of wikis that have been created and used by elementary teachers and students around the country.

a 6th grade wiki
School: Wilson Elementary
Description: a second grade wiki
School: Wilson Elementary
Description: a one year old second grade wiki originally created by the teacher, but largely constructed and edited by students.
School: Discovery Elementary, Buffalo, Minnesota
Description: This wiki is designed as an interactive space for students who record their daily assignments, collaboratively write wiki-books and engage in discussions about books they have read and enjoyed. Feel free to contribute! Go to the blog link to see posts about classroom happenings, or to listen to podcasts done during a monthly Senior Citizen/student collaborative writing project.
District: Woodward Academy
Description: Created by third graders during a unit study of pioneers and the westward expansion.
School : Deira International School, Dubai
Description : Work created by students based on the book by Louis Sachar
Topic : Analyisis of the book, and some activities based around the themes of the novel
School: Pocantico Hills School, Sleepy Hollow, NY
District: Pocantico Hills School District
Description: Five 5th graders and I created this wiki - our first - chronicling our journey through the book, The Hobbit. It was quite an exciting experiment. While we are now finished with the novel, we still go back and add new ideas to our wiki. It includes writing assignments, multimedia projects, and discussions.

School: Eleanor W. Graham Middle School
Description: A place for students to access homework, science/math related interactive websites in class , communication with parents on ongoing or past projects, (more to come)
Topic: Math and Science
School: Nettleton Magnet School, Duluth, MN, U.S.A.
Description: Welcome to Mr. Monson's grade 5 classroom wiki. Each month I post a question for people to answer. We hope to collect 1,000 things on our list each month. Check out our other online spaces as well!

School: San Miguel Elementary
Description: The world is our classroom. We are a group of 2nd and 3rd grade students who are sharing what we are learning with the world!

School: Carl Sandburg Elementary School
Description: A class wikipage where parents and students can access information about what is happening in the classroom. We have a homework page where homework information is posted, a link page where students can find game links and informational links about the units we study in the classroom, a page where student work is posted for parents to see, a poll page where students can respond to weekly post during the school year. Also (just added) a Just for Teachers page. On this page you can find a list of helpful links that you can use in your classroom with your students!!

School: Twin Chimneys Elementary, O'Fallon MO U.S.A.
Description: A classroom website under continuous revision. Mostly used for classroom management at this point, but will also be used for publishing student work. Created with pbwiki.

All these sites were taken from
http://educationalwikis.wikispaces.com/Examples of educational wikis
There are many more examples of educational wikis on the site that range from elementary to college level. Check them out!