As one option for their final project, students can collaborate on a web project, a presentation, a wiki, a paper--whatever best suits their analytical purposes. The requirements are the same as they are for a person doing a paper or project alone; the students don't have to have twice as much information or twice as many pages even if there are two of them. All members of the group receive the same grade, and they know this going into the project. And the writing tends to be better, too, perhaps because they're working together.
I suspect that the students think something like this: "If we pair up, or work in a group of three, that's only one-third the work for each of us! We've outsmarted her."
I know that I think something like this: "Four fewer projects to grade because they've collaborated? Hallelujah!"