Sounds like permission issues. Check that you have write access to the configuration.php file.
When i want to edit the global config on the site i'm getting an error message saying "An error has occured unable to open config file to write" I've logged onto the server locally and tried through this way and it appears to accept the changes but then when i check the global config again its not saved the relevant changes.
Try setting teachers up as Authors and the user that wil check and OK the content as a Publisher
The idea behind this Joomla site is that each department in the school gets a user logon and password to edit their own area of the site. We want the teachers to be able to add and edit content but the content has to be OK'd by another user before it goes live onto the website but i'm getting confused with the different user groups and who needs to be in what group to edit and make changes and so on?