Every year Roosevelt High sends a group of students to a European city to "study" for two weeks. This trip is discounted to a group price allowing each student to pay their way to whatever city they will be going too. Last year it was Florence, the year before that Vienna, but this year it's Paris.
The students sent are usually the smartest, or most athletic students the school has in attendance. However each year the school selects one female and one male student and pays for their entire trip and gives them a bit of spending money.
No one knows how the school selects these students. All they know is that the principle has the last say.
Secretly for the past few years the principle has been running a sex contest among his female students. Once they express interest in the trip and he feels "safe" with that student he allows them to compete.
Using a rating scale he judges them on several skills and rewards the trip to the one with best score. What they do not know however is that while they will have to have sex with him they may also have to have sex with each other.