Why have a class wiki? See from http://langwitches.org/blog/

Once you are a member of Wikispaces, you can create your own class wiki.

Click on My Account
Click on Create a New Wiki
Click on Manage Wiki to make sure you have an education subscription (free and no ads) and invite people.

From the Home page -
Click on New Page each time you want to create a new page in your wiki
Click on Edit to add content to your pages
Create a Discussion on any page.

More detailed instructions are in this document:

Have a look at these wikis for ideas:

http://5jsext.wikispaces.com/ - Edna
http://5daled09.wikispaces.com/ - Jocelyn
- Fiona

(if you can't get in, ask the wiki owner to invite you)

See Eduwikis for ideas and discussion about wikis in education