There is really not a big difference except for the obvious– Pro has better performance but weighs more and is larger, better for things that take a lot of power. Air is better for normal everyday things, and is lighter, cheaper and smaller, but doesn't have as much CPU power. I would recommend either for students, but if you have a limited budget go with the air. It's more portable, a huge factor in my opinion.
On the website it says the air can only have 4GB ram. That's wrong. These are my MacBook Air specs:
MacBook Air (13-inch, Mid 2012)
Processor: 2 GHz Intel Core i7
Memory: 8 GB 1600 MHz DDR3
Startup Disk: Macintosh HD
Graphics: Intel HD Graphics 4000 1024 MB
Storage: 500GB Flash Storage
It runs OS X Yosemite Version 10.10.2, planning on upgrading to OS X El Capitan today.
I also have Windows 8 installed through Boot Camp