When Wu, the radio co-host, first volunteered to lecture in schools in 1992, she was often rejected immediately. She now speaks at about 50 schools a year. "The people in the Education Ministry are already more open than they were 10 years ago," she said. "But they still can't keep up with what students need."

It's no better at home, where parents who have had no sex education themselves don't understand why it's necessary.

Zhang's second book, "Roses Hidden in a Book Bag," published in 2004, is full of stories of high school students having unprotected sex and parents unable or unwilling to discuss the issue. Zhang is now working on a third book, about sex and middle school students. The students featured in her first book were born in the early 1980s, and they prized their virginity and worried that too much sex was harmful.

One boy told Zhang he was in elementary school when his mother slapped him after he accompanied her to a museum exhibit and asked what a penis was. Back home, his mother demanded, "How can you get married if you act like a hooligan at so young an age?"

"The most important thing is Chinese traditional ideas about sex," Wu said. "You cannot tell exactly what sex is. And that is exactly what the students want to know. China used to hide this subject under the table. They considered it dirty, and changing attitudes takes a long time."

In the absence of frank discussion, teenagers turn to the Internet or easy-to-find adult videos. Most of the 600,000 registered users of the sites in a large online pornography case were juveniles, prosecutors in Shaanxi province said. Eight out of nine suspects charged were about 20 years old.

High school and college students in urban China increasingly accept premarital sex, surveys show. While the majority remain more conservative than their peers in more developed countries, Chinese students are having both sex and abortions at increasingly younger ages.

Now, at the close of summer -- after holidays that gave female students time to see their boyfriends -- gynecologists say they expect to see a rise in the number of unwanted pregnancies. And many of those girls and young women will seek abortions.

Some experts attribute that to widespread advertising describing abortions as cheap and painless. Only hospitals are allowed to prescribe the RU-486 abortion pill, but it is easily obtained from illegal clinics for about $15.

In Shanghai, a hotline for pregnant girls that opened last summer was immediately flooded with calls, including from girls as young as 13, according to the Shanghai Youth Daily. A year later, the hotline has handled 11,000 calls; 47 percent of the cases involved first-time abortions, 35 percent second abortions, and 18 percent of the callers had had three or more abortions.

"All these surveys are compatible," Wu said. "Last month, the Beijing Evening News says 90 percent of university students think it's okay to have premarital sex and only 16 percent use condoms."

Girls are too embarrassed to buy condoms and worry that carrying them will ruin their reputations, said Su, the 17-year-old high school student. Boys never think to bring them and don't like to use them, she said.

With her kohl-rimmed eyes, long false eyelashes, blue fingernails and stylishly permed hair, Su looks the part of a rebel. She moved in with her boyfriend, against her mother's wishes. A friend of hers has had two abortions.

But Su said she holds traditional values and is prepared to marry her boyfriend. He is the first boy she has slept with, which she did nine days after her 17th birthday.

At the same time, Su said she already likes someone else.

"For kids our age, dating is just for having fun. It has nothing to do with love. You should have sex and talk about love when you're older, when you have a stable life, a job, a salary, when you understand everything," she said. "I'm too young, I know that."

Researchers Jiang Fei and Jin Ling contributed to this report.

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