As one of the younger members on this site (13) I can see the advantages and disadvantages of this.
I go to a private school, and the most electronic devices we have are smartboards and computers.
The PC's are used in every classroom, and we have two computer labs, one for student research and another for a computer class. The students are permitted to use both labs, but are not allowed to use the teacher computers unless under permission.
We're also not allowed to have electronics, including iPods and iPhones, but in Middle School and High School the teachers get more leniant, I have three or four teachers that don't care if you have it out most of the time.
We have filters up on our internet, but I'm just going to remind you that the only thing a filter does is block the online websites you can access, and not the apps that can be downloaded, and the ones that come pre-downloaded. If youtube is enabled for the school network so that teachers can pull up videos online, that also makes the entire youtube app available, as well as it being available on the Safari browser, because the youtube app feeds off of youtube.com. Simplified, that means whatever you can access on the school internet the kids can access on the iPods and through apps.
There is also no way to remove the pre-downloaded apps without jailbreaking the iPods, and that itself can unleash another whole stream of events.
Apart from kids getting into things they shouldn't be, there's also the kids' responsibility. There's a neighboring school to ours where the kids use iPads, (which are only available to MS and up children) which I think would be a better idea. iPods are so fragile and breakable, no telling what a fourth grader would to do one. And during group projects the kids may fight over who gets to use it, even Middle School students fight over who gets to use the computer on a group project and who gets to make the powerpoint slides...
So, in conclusion, I don't know if this is what you have in mind or not. I think most schools have gone this long without them, it's not necesarry. IT's too much risk for kids that may not be responsible enough, and the fighting over priviledges. Also some fourth graders might decide not to turn in an iPod and keep it. You never know. I'm sure that there would be tracking numbers and costs for missing iPods, but if it's a classroom activity each student wouldn't be assigned a number and there would be no way to tell who took what.
In my opinion, stick with the textbooks and handout papers. This really isn't necesarry.
Also, sorry if I'm rambling. It's 2:21 A.M. where I am and I should really sleep.