I believe there may be a way of doing this in automatic updates in mountain lion but for those of us with an earlier version of OS X it can be a bit more tricky.
Apparently there is a way of doing this thru the server and if anyone knows how to do this please post it on this thread.
However here we have a number of macs with a number of different versions of OS X so I have found a different solution.
First of all download lingon
http://sourceforge.net/projects/lingon/files/This software lets you add commands to launchd - a scheduler (took over from cron) on the apple mac.
Do the usual and copy the app into somewhere like utilities.
Run Lingon
Click on the + New symbol at the top of the screen
Add a new users Daemons
Step 1. Give it a name I used com.softwareupdate.myversion
Step 2. Type the command (Also called what) I put "/usr/sbin/softwareupdate -i -r" i.e. install recommended updates
Step 3. When - I said Everyday just at the end of school.
Saved it and rebooted the machine.
This should work as long as the machine is on even if no one is logged in. (I hope).
Obviously I will now have to go round and do it with every machine!
