On the first Sunday of 2007, Jeri Shoop knocked on her daughter Riley's bedroom door, then barged in. "I want you to take a drug test," she told the bleary-eyed girl, who had come in past 1 a.m. after yet another night of partying. As Riley stomped off to pee on the test strip, Jeri asked what the results would show. "I got so angry," says Riley, now 17. "I got right in her face and yelled, 'Cocaine, okay?!'"

That moment marked a turning point for Riley, pretty and popular, and Jeri, a working, divorced mom, who finally saw that her only child was in serious trouble. Alcohol, pot, coke, ecstasy, OxyContin: Riley had tried them all. She had been skipping school, stealing money and sneaking out in the middle of the night. She had crashed her mom's car at 3 a.m. The high school junior had even threatened suicide. "I was terrified," says Jeri, 46. "And I realized somebody had to put the brakes on."

Like thousands of parents dealing with out-of-control teens, Jeri and her ex-husband Marc Hanson—they'd split when Riley was 9—considered everything from boot camps to wilderness programs to residential treatment centers. First Jeri placed her daughter in a psychiatric ward at Centennial Peaks Hospital. Together, Jeri and Marc settled on a therapeutic boarding school, an increasingly popular option that would allow Riley to continue her education while getting the help she needed (see box). Jeri broke the news to Riley in her hospital room: Instead of returning to Denver's East High School, Riley would go to an all-girls boarding school in Vermont—far from her friends and, Jeri hoped, bad habits. Jeri, a mortgage broker, and Marc, 57, a martial arts instructor, took out loans to cover the $6,000 monthly cost.

Ten days later Jeri and Marc wept as they left a stunned Riley at Bromley Brook, a school in Manchester Center, Vt., that offers around-the-clock supervision coupled with therapy and substance-abuse counseling. "I can't believe they actually left me here," she thought as she unpacked. "I thought it was just a scare tactic so I'd clean up my act."

Back in Denver, Jeri cried herself to sleep thinking back to the happy little girl who once painted her room in polka dots. She was plagued by self-doubt: "Maybe if I'd been around more instead of working so much. Maybe if I hadn't dated ..."

Surrounded by strangers and cut off from drugs and other distractions—personal computers, iPods and cell phones were forbidden—Riley followed the rules, convinced if she did, "I'd be out of there in no time." The real challenge, though, was living sober. "Riley's drug use was more extreme than some girls,'" says her school therapist Sandy Birch. "But she was struggling with the same issues—depression, anxiety, low self-esteem." On Jan. 28 Riley wrote a letter to friends: "I've been sober since the seventh of January. I feel like I am on a drug called Sobriet-x.... Screw it. Screw this place."

Making friends had always come easily to the laid-back teen; she bonded quickly with her three roommates. Lying in their bunk beds after the 10 p.m. bedtime, the girls exchanged stories of how they got there—failing grades for one, sleeping around for another, bad attitude for a third. One night they decided to pierce each other's ears with a sewing needle swiped from the art room. Riley offered to go first. (Later, Bromley Brook banned earrings.)

Eager to earn privileges like extra phone calls and supervised trips off campus, Riley stuck to the schedule—7:30 a.m. wake-up, breakfast, morning meeting, then group or individual therapy before classes. That system, says school executive director Laura Mack, "is intended to teach students to live within limits."

For Riley, that was a big change. Her parents had broken up and gotten back together several times before they separated for good. Afterward, Riley bounced between Jeri and Marc as they went through a series of relationships and juggled busy jobs. Home alone in Jeri's yellow brick bungalow with a list of chores, she decided hanging out was more fun. Says therapist Birch: "Riley and her mom were more like peers than mother and daughter."

With Riley safely tucked away in the Green Mountain foothills, Jeri had been thinking about just that. Replaying late-night scenes between them, she wondered why she'd swallowed Riley's lies when she'd come home with bloodshot eyes, reeking of smoke. "I was in denial," Jeri says. "When I did confront her, she'd throw a fit. I was weak." Now, on her five-mile morning runs, Jeri had to hold herself back when she'd see teens smoking pot in a park. "I wanted to shake those kids and say, 'You're going down the wrong path!'"

Back at Bromley Brook, Riley was taking a hard look at the road she'd gone down. After an emotional group therapy session, she wrote in her diary, "When I think about all the sneaking and lying I've done, I hate myself. I hate that I lost my virginity at 14. I hate that I blacked out. I want to be able to wake up in the morning, knowing I had a good time AND remembering it." Over the next few months, she got A's, worked hard in therapy, attended off-campus AA meetings. She even started an activist group to help Darfur.

Then she did something crazy. Using a friend's ring heated by a flat iron, Riley branded herself on her hand and hip. "It was," Riley says, "an impulsive act." When her therapist asked about the hand, Riley first made excuses, then confessed; she lost phone privileges and off-campus trips. Back home, the bad news had a familiar ring. At 15, Riley had started cutting herself; Jeri got her into therapy, and the behavior soon ceased. Now, Jeri wondered, would Riley throw away all her progress?

The answer turned out to be no. Riley got back on track, earning good grades, going home for her 17th birthday in July and passing her drug tests. In August she and six other girls went on an overnight therapy retreat called Gateway. Huddled in a farmhouse on a hill, the girls talked, often tearfully, about wanting to change. "I'm tired," Riley said, "of justifying my actions when I know they are wrong. I'm tired of messing up."

But as graduation approached and her therapist started talking about transition plans for life back home, Riley began to feel depressed and scared—and she messed up again. One mid-November afternoon, after attending a college-prep course in town, she stopped at a convenience store, bought two six-packs and downed six beers, hiding in a bathroom stall with two friends. "I felt invincible," she says. "I was excited and nervous at the same time." Two weeks later she admitted what she did and called her mom. "I felt like I'd been punched in the stomach," says Jeri, who watched other parents in her neighborhood attend lacrosse games and send their kids off to the prom. "I felt I'd wasted my money."

Still, Jeri was sure of one thing: Riley would come home to a tougher mother. To prepare for her daughter's return, she went online and bought 500 at-home drug tests and a Breathalyzer. After talking to her therapist and teachers, Laura Mack ruled that Riley could graduate. "I'm not in the business of ruining lives," she said. "Hopefully, this will just be a blip. Riley's come a long way."

On Dec. 15, inside a Vermont church, Riley, wearing a white dress, received her diploma along with three other girls. She looked at her proud parents as she spoke: "As you know, I am terrified of my future ... but you've assured me you will help me through everything." Jeri and Marc both took a deep breath. "She has turned things around," Jeri thought.