I am a third grade teacher and our class has recently built a three chambered compost bin for the school. Any advice on how to proceed?

You may well find some useful albeit basic info on our web site. There are also dozens of great school/gardening links that will be helpful to you. Congrats on teaching kids about Nature!
John
Ecologicals
http://www.ecologicalsgardens.com/

Each child could ask their care giver to save scraps for the bin such as remains from fruit or salads. But only uncooked natural items. It should fill up in a hurry.