AT the college where I work, most computer labs that were deployed a few years ago were locked down very tight. Basically all the students could do is use an approved set of programs, and Internet was blocked off. During that time, the computers were vandalised regularly and on a large scale. Students would unplug them for fun, smash the keyboard and scribble on the screen. And yes, we're talking about yound adults.
Magically, when the restrictions were eased, and unfiltered Internet access was allowed, vandalism was reduced dramatically. Instead of wasting their time vandalising the school's equipment, the waste it on Hotmail or Facebook.
Moral of the story, the best way to have students take care of computer equipment is to make them feel as if they own it...
With that said, I still agree that giving every kid a laptop at school is a baaaaad idea. Any sane teacher would strongly oppose this plan...