Honestly, I do not see the difficulty of making samples of photos with "CONTACT SHEET" in Photoshop. Basically, you set up in 2 minutes, waiting for the computer do the work in 30 minutes after you spend a few minutes to save each sheet in JPEG. As for the final assemblies, is something I really do not like doing, and I'd rather pay a local store photo developing, can do the graphic art.
It isn't just 'create a contact sheet', it is the top to bottom management of the process of putting out pricing to the students, collecting the orders, getting the shots done, making sure you have all your names to faces and then the final packaging. Lots of moving parts when there are 300 students.
I found a thread that may apply: http://www.eventphotographersociety.co.uk/forum/showthread.php/5976-fotovelocity-com
It mentioned http://www.timestonesoftware.com/ as an option with offices in the UK/EU.