Spend a few minutes and read my topic,
Brand new Horizontal nipple water system for a really old coop! That is exactly the kind of system I have on my old coop. 55 gal barrel collecting rainwater and feeding 5 Horizontal Nipples (best water nipples on the market in my opinion, links in my topic) in the coop to water 28 birds right now. I mounted my barrel on the side about 10 years ago and set it up with a clear plastic pipe between the bungs to show the water level. I have a piece of a brass scrub pad stuffed down in the top tee to allow air in and out and stop mosquitos from nesting inside. I live in mid Georgia and seldom have to worry about freezing and in all the years it hasn't been a major problem.
One thing you have to do to set your barrel up like this is find both bung plugs with the 3/4" pipe thread inside. Usually only one of the bung plugs is threaded in the middle and the other just has a cover over the hole, the right bung plugs can be found if you look around enough. You also need to design a way to drain all the water from the very bottom and I finally found the right parts to do it with, Google search for Uniseal.
It would be real easy to build a system out of PVC and put a hose fitting on one end and a drain cap or plug on the other end for cleaning especially since your rain barrel already has a hose bib on it to hook a hose to. Home Depot has PVC fittings to attach a hose to, generally in the same area with the RainBird sprinkler parts, this is what they look like,
http://www.homedepot.com/p/Orbit-3-4-in-Slip-x-MHT-PVC-Fitting-53361/100119737#.UhMBRSnD_rx They have both male and female hose in 1/2" & 3/4" pvc slip or thread, what ever you need.
Since this is for your school, I would be more than happy to help all I can with your project. Send me a Pm with your questions and maybe include your email for easier communication and I will help all I can and maybe send you some parts if you can't find them.