I'm the one who assigns my students 5-6pp. papers. And I'm the one who goes out of her way to explain that what this means is that each paper should probably be substantively onto a fifth page--with no funny stuff done to the margins or font size.
So why is it that, as I work slowly and grimly through a stack of essays, I sigh and grumble every time I see one that fills a full six pages. . . and perk up every time I see one that's three and a half?