First of all... no one gives back an ipod. And that silly little security thing is just that- silly. Anyone knowing basic electronic skills can break that... there's even a hacker program especially for it. And apple products are a snap... why do you think there are so many bootleg ipods? They're easy to break in to. And even if he or she can't, it's simple enough to sucker some fool into buying it, open or not.
Personally, I always write down the serial numbers of my devices. It may seem silly, but look at it this way- an ipod is expensive. It was lost on school property. If you have the serial number, some schools will check everyone going out of the school, and if they find the number, well, there's your ipod. But there's really nothng that a school can do otherwise. Without that id number, they'd have to let you manually try and enter a password, which of course could emss up another students property, and most teachers don't want the liability.