Oh ok well I am guessing you will not need the 15'' Pro because they would probably be telling you otherwise if they needed you to be able to run high-end production software, etc. that you really need a more powerful computer for. I would assume that any computer in Apple's lineup will be adequate for you since the main requirement seems to be that you need OS X.
Even the cheapest MacBooks have plenty of power for basic office work, powerpoints, etc. I would go with the 13'' Pro as it is slightly more powerful and doesn't lose much battery life over the MacBook Air and you get the retina screen. The Pros have more ports, etc. for attaching to projectors, using external storage, and so forth compared to the retina MacBook so I'd take one of them for a school setting. Retina screens are really nice screens to work on as well. The 15'' Pro will of course do everything but it is much more expensive so unless you really want that larger computer, I wouldn't recommend it over a 13'' Pro.