Absolutely a laptop... He'll want to take it to the library, the coffee shop, classes, outside and everywhere else for group projects, convenient access to other resources, and changes of scenery.
I vote laptop, but if you go with a laptop, there are a few things to warn him about:
First of all, speaking of Coffee Shops, make sure he knows:
absolutely no food or drink within three feet of the laptop, for any reason, even for "just a sec". I work at a school myself, and we see liquid spills that (best case scenario) ruin a keyboard or (worst case scenario) fry the entire computer for good if it leaks down onto the motherboard. The school here uses a brand that has the full accident/spill/drop insurance, but the one thing that saddens me about Macs is that they don't offer that. I can understand why, smaller market and so on, but until they do, tell him to be very, very careful with it. We try to warn people as much as possible, but since we have seen spills, even from teachers, it always bears repeating.
Favorite spilled item, damaging a computer: Ranch dressing. Usual suspects are Coke, tea, water, and Gatorade.
Most impressive spill, scored on artistic impression: One of our students had a big pitcher of water on the tall bookshelf above his desk above the laptop, and when he slammed the door behind him, he heard a huge splash...

one of those times where he didn't even want to go back into the room because he knew exactly what just happened.
Just get him a secure cable lock to help prevent it from being stolen and he'll be fine.
Definitely. These things have legs and can "walk away" if you are not careful, especially at a place with a lot of people milling around, like a school. Make sure you have something by way of insurance... and there are actually places that can track a stolen laptop, but I can't remember off the top of my head.
Also.. some sort of good case or padding to protect it-- next most common form of damage here is jamming the laptop into a backpack, putting in books, squeezing it, shoving in more books, squeezing it, putting in more books, and crack! There goes the screen....
That being said... if you take care of it, a laptop is
great. I had a desktop and breaking everything down and reassembling it every time I moved-- which was often-- really got to be a huge pain. Once I had a laptop, I don't really see myself buying a desktop again, for what I do; most laptops today have plenty of capacity and power, unless you do serious video or tons of photography. In that case you should be making backups onto another drive anyway, so storage is not as much of an issue unless you know for sure, without a doubt, that you will definitely need a lot of it.
P.S. Sorry if this was long-winded... I do computer repairs, and if this prevents even a few accidents, tech people like myself everywhere will be extremely grateful. Forewarned is forearmed, and all that stuff.