I think it often doesn't work. For example, just last week our teacher set us an assignment to research a particular aspect of Yeats, and she would then photocopy it all out. I got around 80 pages all up. No less than half of this was the Wikipedia article for Yeats, printed many times.
Depending on the exact nature of the task, these are the problems.
1. Everyone does a little too much and so you end up with pages and pages of stuff you'll never read.
2. Some people do bugger all because they know they can use others'.
3. It's really repetitive. Do they think that they can give 30 people the same assignment with each having unique ideas?
4. If you've actually been taught the same stuff, then it's generally more beneficial to use your own notes.
But I guess it can work, like jackattack's school, and sometimes if, like, they give us an assessment and mark it but hand out the best one to everyone.