Did you previously register your iPod with Apple? If not, do you still have the box? The reason being is that the original box has the serial number. You need to register that with Apple so that their computer system will be alerted anytime anyone else registers an iPod with that same serial number (something of which you can't fake).
I would also see what your home owners insurance (or your parents'/parent's) will do. Unfortunately there isn't much your school will do (if it is a public/private mid-high, junior high, or high school) as most of them have a strict no iPod policy (something of which students should abide by). These no iPod policies are in place for a reason. It stops students from ignoring teachers and it stops other students from taking property that isn't theirs.
So that is about it. Call Apple and your (or your parents'/parent's) home owners insurance. More than likely the insurance company will be able to replace the iPod but it might cause an increase in the monthly costs and/or the premium. Learn from this lesson though and never take an iPod to school again. You just can't trust people with something as valuable and as popular as an iPod. Back when I went to high school, I carried around a Rio 600 (a player with a 32MB capacity, that was pretty large for the time). I had just purchased a $250 64GB memory module for it upgrading my player to a full 96GB of memory (this was 32MB higher than any other player on the market, this also really dates myself). The player itself was $250 so I had $500 sitting in my backpack. Some student decided to take it from me. It took a few days but I finally tracked it down, did somethings I can't repeat here, and got my player back. Point being: people (especially students, no offense) will always be like this.
64GB iPhone 5 | 64GB iPad mini | AppleTV 2 (2012) | AppleTV 2 (2010) | 2012 15" MacBook Pro, 1TB SSHD, 16GB DDR3 1600 MHz, OS X 10.8.3 Mountain Lion | Apple Lossless | iTunes AAC 192kbps VBR | iTunes 11.0.2| Library size = 1.04TB | Legacy iPods: 3G 40GB, 4G 40GB, 5G 60GB, 160GB iPod classic (2009)