This is an anecdote from when I was in elementary school and takes place around 1999-2000. Windows computers were just being installed in the classrooms. The mechanism that locked down the computers initially was system policies. You could screw around with a limited number of settings and applications on the system, but a lot of stuff was restricted.
However, one day in the school library, a new computer didn’t have such restrictions in place. Our 7th grade teacher (resident IT technician) had just finished setting up DeepFreeze on it, and challenged my friends and I to try to break it. We tried everything, like deleting all we could in C:\Windows, but it all came back magically after the reboot. I must admit DeepFreeze worked very well.
That was my first encounter with DeepFreeze, but that was definitely not the last. The computers in my high school had DeepFreeze installed. The public computers in the Vancouver Public Library are also locked down with DeepFreeze.
DeepFreeze works by redirecting all changes to the contents of a hard drive to another location, which is wiped upon a reboot. Obviously I didn’t fully understand how this worked back in 6th grade. But in any case, it’s very effective and very difficult to bypass!