Sarah Van Zanten, 15, was lying on the floor, an ice pack on her aching ribs. For a moment, she had no idea where she was; then her boyfriend's face came into focus. They were at a party, and Joe (not his real name), the cute football player she'd been dating, had kicked her, hard, propelling her into a wall, where she had hit her head and blacked out. "I woke up and he was hovering over me," Sarah, now 18, recalls. "I just wanted to get away."

Just four months earlier, Sarah thought she'd found the perfect boyfriend, ready with corsages, compliments and movie dates. Quickly, though, sweet talk gave way to insults and demands and, finally, physical abuse. Within days of the Feb. 12, 2005, kicking incident, Sarah, a willowy strawberry blonde with a spray of freckles across her cheeks, stood in line at the family division of the Santa Clara County, Calif., court clerk's office, waiting to pick up a copy of a restraining order. "I never would have thought," Sarah says now, "something like this would happen to me."

Once a hidden problem, teen dating violence is getting some serious attention. A 2005 study by the Centers for Disease Control and Prevention found that of 6,888 high school girls surveyed nationally, 1 in 11 had been hit, slapped or punched by an intimate partner. According to a Harvard study of 4,163 public high school girls in 2001, nearly 1 in 5 reported physical or sexual abuse in a relationship. "This is a major adolescent health issue," says Jay Silverman, associate professor of society, human development and health, who directed the Harvard study. "It affects [girls'] academic lives, lowers their standards for relationships and puts them at great risk for unintended pregnancy and STDs." No one knows what causes such behavior—theories range from violence in the home to alcohol and drug abuse; others suggest violence in movies and the Internet may play a role. What is clear: Boy abusers and girl victims, without help, are likely to repeat those roles as adults.

Getting hurt was the furthest thing from Sarah's mind when she met Joe at a back-to-school dance in September 2004, the start of her sophomore year. "He was really cute," Sarah recalls, grinning. Within weeks she was in love. Every afternoon she would sit on the front lawn of her house in a suburb of Palo Alto, Calif., hoping to catch a moment with Joe as he walked home from practice. "I was crazy about him and about being in a new fun relationship," she says. Soon the two were inseparable. Joe, knowing Sarah left before dawn for crew practice—she eventually became team captain—began sending her text messages at 4 a.m. "They would say things like, 'I know you are at practice right now, but I just wanted to be the first one to say hi,'" Sarah says.

Initially flattered, Sarah gradually grew uneasy with Joe's possessiveness. "He never really straight out said he didn't like my friends, but he made it clear I didn't need anyone else. If a friend called, he'd be like, 'Why do you want to go out with them?'" When she did find time for pals, there was hell to pay: "My phone would ring and my friends would say, 'Why don't you ignore it?' And I would say, 'I can't ignore it—I'll get in trouble.' If I was hanging around with anyone else, he'd get mad and yell at me on the phone." Her friends knew only that something had changed. "I was seeing Sarah less and less," recalls Jeremy Carlson, 18. "It became kind of a joke—that she was too busy with school and crew."

Sarah kept her doubts to herself. "I felt ashamed of sticking with him," she says. "I think it has to do with being in one of the first relationships of your life. You don't really know where to draw the line." And then there was Joe himself, who followed up his outbursts with fervent apologies and tokens of love, usually bouquets of roses. "I got a lot of flowers," Sarah recalls. "He always delivered them to me himself. It made me feel loved."

But her parents, Kate and Mark, a computer