"Sociologists have mapped the romantic and sexual relationships of an entire high school". According to the article,

...[T]hese adolescent networks may be structured differently than researchers previously thought.

The results showed that, unlike many adult networks, there was no core group of very sexually active people at the high school. There were not many students who had many partners and who provided links to the rest of the community.

Instead, the romantic and sexual network at the school created long chains of connections that spread out through the community, with few places where students directly shared the same partners with each other. But they were indirectly linked, partner to partner to partner. One component of the network linked 288 students - more than half of those who were romantically active at the school - in one long chain.

Here's a nice graphical representation of the sexual network. (Via Boing Boing.)