You'll need to use Google Apps Team Edition for this. The username for the other people in your group is in the format firstname.lastname@ridgewoodschool.co.uk. One person needs to create the presentation (the envoy) and then invite others to collaborate on it.

Mr Belshaw can see who created what using the 'History' tab. Make sure you do the work and are ready to present on Thursday 23 April 2009!