"Well, you can make the site private so only a certain amount of people can view and join your site. For example, a private site only allows people you invite via email to the site so they can view it. To make a private site, you need to be an administrator or above. Then, you need to go to settings, permissions, and change it to private, so only members you invite via email can join and view your site.

Also, to prevent people from editing tables, you can set the site permissions to invite only. This allows you, as the creator, to decide who you want editing your pages. If you want people editing pages, you can make them writer or not. If you do not want your students editing pages, leave them as registered users. To change it to invite only permissions, go to settings, permissions, and change the editing permission to "only people I invite". This will stop members from editing pages unless you promote them. "

"I want only current students to be able to edit pages, it's why I chose a wiki. It's the former students i'm not sure what to do with."

"I would have all the students cancel their membership to the site on the last day of class (or whenever it's appropriate). That way, you don't have to manually go through and ban each user or change their permissions."