Ok here's a suggestion...
I'm assuming that your LAN is 'hubbed' around a server.
If you can run or are already running an AMP system (Apache, MySQL and PHP), you can quite easily set up a Moodle LMS (Learning Management System).
With a relatively steep but short learning curve, you can set up regular tests for your students with all the results stored on the MySQL database. The tests can be multiple choice, open cloze, short answer, essays, etc. or any combination of test types. The tests and activities can be timed and you can also incorporate images and audio in a basic way.
I've successfully set up some Cambridge CAE practice tests for my students and I'm getting some very positive feedback from them.
I'm a developer so this stuff is pretty easy for me. I understand that all this seems a bit daunting for someone without much IT or development experience. Moodle is very well documented and there's a lot of people out there who can provide support.
Oh yeah, and one very important detail - Moodle is Open Source which means that it's free for you to download, install and use and if you want to do anything specialised with it, you can hire a developer to make the changes or write the new code for you.
http://moodle.org/
Hope this helps.
