This is a MUST TRY site. It's not often that I'm amazed by an educational resource, but I am with this one.
Pora Ora is a stunning educational virtual world for Primary school aged students. Play truely fun educational games which practise skills in English, maths and many other subjects. The graphics and useably is superb.
Online safety is at the heart of this site. The parental admin account can set the student's account to free chat with everyone to completely locked down where they have the world to themselves and everything in between. The site has a language filter and users can report any incidents of trouble. Also, the first task requires the user to complete an online safety task.
The site is free with a few premium features coming out later. You have got to try this one!