One of the problems I am finding in our school district is finding both a wiki site that can be kept private and does not require a student email account to sign-up. Well, I have come across a rather simple one, called Jottit.
It is very simple to use, although it is a tad unconventional to create the classroom wiki. First you type in some sample text to create the site, next you choose settings to create your unique URL, and then you simply put in a password to claim your site. It is at this point that you are able to choose the option to require the password to both edit and view the site. This allows teachers to have a classroom wiki that is only accessible to students who have the password and students do not need an email address to sign-up.
Just in case you were running into the same frustrations we were...
Kathy Schrock | Jottit