Why not have the grade of papers be multiplied by the inverse of the plagiarism score? For example, your first author would get a maximum of a 3% grade on his paper. Of course there are false positives to think of as well, but this would force the authors into more and more original content.
The very first assignment I did in college was my own, some code I wrote for a programming class. I turned it in, but my friend was in the class didn't do his assignment. I figured it was a basic enough problem and I really just turned in the assignment for him. We both got slaps on the wrist, but I never blatantly plagiarized again. I'm not saying I've never reused a sentence from another document on occasion, but usually it was either cited or more unconscious.
The big bummer in college was exactly what he talks about though: the propensity for students in some sort of group to help each other out. The fraternities and athletes were always the worst offenders. For the general eds, everyone in class knew that so and so had a copy of this professors test which he barely changes from year to year, or this fraternity keeps all their papers from previous classes categorized(!) so other members can use them, and that sort of stuff.
Because Turnitin is pretty terrible software and there are a lot of false-positives. I remember having to "explain myself" for an essay I wrote where what was copied was direct, cited quotes. It uses word pairs sometimes and will highlight any uncommon phrasing that someone may have used in the past.
The very first assignment I did in college was my own, some code I wrote for a programming class. I turned it in, but my friend was in the class didn't do his assignment. I figured it was a basic enough problem and I really just turned in the assignment for him. We both got slaps on the wrist, but I never blatantly plagiarized again. I'm not saying I've never reused a sentence from another document on occasion, but usually it was either cited or more unconscious.
The big bummer in college was exactly what he talks about though: the propensity for students in some sort of group to help each other out. The fraternities and athletes were always the worst offenders. For the general eds, everyone in class knew that so and so had a copy of this professors test which he barely changes from year to year, or this fraternity keeps all their papers from previous classes categorized(!) so other members can use them, and that sort of stuff.