Oh poor poor naive Claire, take it from someone who's worked (Okay maybe "worked" isn't the right word, whatever you want to call high school library student aide.) in a school library for two years: the whimsy feeling of being in a library will fade quickly. There is pointless babbling in the form of any students actually in the library for anything but last minute homework, from the same group you get your running and yelling, and the idiocy is a given. Or maybe that's just because I worked in a highschool library. Although Claire is right, there is more than just stamping books and shushing people. There's shelving. Endless shelving of book after book till you notice trends in the check out patterns and start wondering who the hell is checking out so much Anne Rice. There's also stamping and barcoding upwards of 50 textbooks. And no, they won't let you shush people, that's the librarians job, you'll be busy shelving or hiding from the librarians so they think you're shelving.
That all said I did learn how to shelf by the Dewey Decimal System and how to juggle paperbacks, sadly I can't list that as job experience since it wasn't a job. Woe is me.