Restoring Windows 7 to previous point in time

Hi,
I need a help with problem concerning restoration of windows to a previous point in time. At wok (teaching computers) I need to create some sort of backup that would allow me to restore computers to state they were before each class started (because people are capable of making terrible mess in folders that I did not even know existed).

Simply put, I need something that will give me clean system with software I installed and delete everything else.
I was hoping to use restore point, but sadly it does not work as I think it did in XP and it does not delete anything users created

Thanks for any tips

If anyone cares, this is the list of installed software

• Windows 7 Pro x86
• Office 2010 Standard
• avast! Antivirus
• Firefox
• Chrome
• Accounting software
• iTALC (software for teachers to see what are student doing, locking them out, etc)

Thanks for reply,
I was thinking about using system image, but I was just wondering if there was another way that would not take up 5 DVDs. Something like a program that would keep a "change list" and then it would revert everything on it.
As for the guest account, I still need to keep data people create there for the duration of their class (Excel spreadsheets for example), so I guess I will do the System Image
Thanks

DVDs are definitely not the method of choice for storing images. Best to use another hard drive. I'm guessing these machines have no other hard drive, in which case you would need to use a separate partition on the existing hard drive, since images cannot be stored on any partition contained in the image.

Stored images typically require roughly half of the occupied space on the partitions in the image---an image of C with 30 GB occupied might take up 15 GB, so that separate partition would have to be at least 15 GB in size.

ignatzatsonic:
Yes, the computers have only one HDD with single partition. And I was thinking either DVDs (which I though are stable enough) or some smaller external HDD or flash disks for it.

Brink:
I may look like a total ignorant (I will admit it, I do not reinstall or restore Windows that much, maybe once in 2 years), but couldn't I use single system image to restore all computers and then just change names and product key? Student computers in class are basically all clones of each other, just with different name and product key

Every single computer in classroom is exactly the same, down to every single piece of hardware
User accounts are the same (Teacher (admin, PW locked) and Student (regular, no PW)), anti-virus is using group license file, and iTALC is also using only one key file identical to all computers.
And deleting all different files and setting was the original idea :)