It was just after sunset on a warm day at the College of New Jersey. Under a rising moon, the soccer team ran the field in the lighted stadium. Outside the student union, a guitar duo played an acoustic set. And in a dormitory lounge, 27 freshmen sprawled on couches as psychology professor Elizabeth Paul quizzed them about their sex lives. There was hardly any talk of "dating" or "boyfriends" or "girlfriends"--this is 2004, not a rerun of "Happy Days." Instead, the students and the professor talked about "beer goggles" and what happens when partners "catch feelings." Even as freshmen these students know enough about "hooking up" to hold forth for more than an hour. As they dished, Paul scrawled in her notebook. Their musings may contain the spark for her next big research project.

Since the late 1990s the media has been filled with accounts of adolescent hookups. The phrase describes one-time sexual encounters--anything from kissing to intercourse--between acquaintances who've no plans to even talk afterward, let alone repeat the experience. As alarming as this sounds to parents, journalistic accounts of this behavior seem sketchy and anecdotal, filled with boasts by kids who won't give their last names. Now that's starting to change. In the past few years social scientists like Paul, the 41-year-old chair of the College of New Jersey's psychology department, have started aiming their microscopes at hookups. The result is a growing body of peer-reviewed research that feels like a cross between the Discovery Channel and MTV's "Real World." The researchers' aim: to find out how and why kids hook up, and how it affects them emotionally.

The early research confirms just how widespread the behavior has become. In 2000 Paul published what colleagues credit as the first academic article that explored college hookups in depth. Her survey of 555 undergrads found that 78 percent of students had hooked up, that they usually did so after consuming alcohol and that the average student had accumulated 10.8 hook-up partners during college. Studies on other campuses produced similar numbers. Researchers at James Madison University found that 77.7 percent of women and 84.2 percent of men had hooked up, a process they said routinely involving "petting below the waist, oral sex or intercourse." At the University of Michigan, more than 60 percent of students reported hooking up; they said that a typical hookup more often included "genital touching" than "a meaningful conversation."

Skeptics ask whether hooking up is really any different than the one-night-stands college students have had for decades. Most researchers believe it is, but it's hard to prove. The difficulty stems from the fact that older research focused on "casual sex," usually defined as an encounter that includes intercourse. Since many modern hookups stop short of all-the-way sex, it's hard to make apples-to-apples comparisons. But the academics say they're convinced the phenomenon has changed. "It's generalized... now it's the campus norm," Paul says. "If you're a normal college student, you do it." While it's impossible to say exactly why students would rather hook up than seek traditional boyfriends or girlfriends, students say that greater competitive pressures--to build a resume, position themselves for grad school and chart a career trajectory--leaves them little time for romance. Says Michigan professor Monique Ward: "[They say] 'College is just a layover--I don't want to be tied down and committed'."

Those sentiments weren't apparent in Paul's focus group last week, probably because the students had just arrived at college. The group's more vocal participants happily discussed their motivations and the emotional fallout of their high-school hookups. Some said hookups often left them feeling lousy--especially if they'd suffered beer goggles (in which drunkenness led them to a substandard partner) or if one hookee caught feelings (meaning they became emotionally involved). When Paul asked how they defined a "good hookup," one young woman quickly answered: "When no one finds out about it or talks about it later."

Now that early studies have quantified the frequency of and sex practices that take place during hookups, researchers are becoming more interested in the emotional aftereffects. Some researchers are doing longitudinal studies that follow the same students from freshman year onward, to see how their attitudes change. For her current research Paul is asking more questions like "Do you think your hookup experiences are going to help you be a good relationship partner someday?" The students don't really have an answer. Some researchers worry that hooking up gives students sexual experience but no real relationship experience, which could affect their ability to segue into more adult, committed relationships. But Allison Caruthers, a Michigan Ph.D. student who's doing her dissertation on hooking up, cites research showing that people who've experimented with alcohol or marijuana are often psychologically healthier than people who abstained entirely. She believes there's a similarity in hookups. "People are looking at hooking up as this horrible, wretched thing, but some experimentation may actually be positive in terms of the way you think about sex and relationships," she says. For the freshmen gathered in the lounge last week, the next four years offer plenty of chances to learn those lessons.