I agree. You'll definitely need a laptop for school.
You'll at least need MS Word and Excel for Mac, and MS does not make a version (ios) for tablets. There are apps, though, that you can get to transfer work you'll have done on your laptop onto and useable on ipad. Your work will be too
MBA is light and great looking, but our family still likes the idea of having a cd/dvd player that you get in a MBP. (One of my sons just finished college and one is a junior.)
If money is an issue, and isn't it usually, you might consider buying refurbished from the Apple website, and for a little more than the cost of an MBA or MBP you can get an Air or Pro laptop and an ipad2. We recently bought two ipad2 64's. They come with a new outer shell, new battery, and full one year warranty.
Also, if your college/university is listed on the Apple Education site, you get a discount on new products.
And, as was suggested, check with the school. A few weeks before my son went back a few weeks ago, he got an email saying he had to have a laptop for class. His ipad can do all he needs for class.
An advantage of an ipad is it can greatly reduce schlepping books everywhere as many, many texts are now available to buy or rent electronically.You can have it on your laptop and as far as I know transfer it to your ipad for class. If you want only one, the MBA is lighter than an MBP for carrying around.
Hope this helps.