Cao Yonghong's 14-year-old daughter, Lily, told her that a man who sat next to the girl on a bus last year kept asking to connect with her on the Chinese instant messaging app QQ.

The information worried Cao - a lot.

"My daughter didn't know how to deal with such harassment," the 47-year-old college teacher from Southwest China's Chongqing said.

"I also thought that it was necessary for her to have overall sex education, not just basic physiological knowledge but awareness of psychological changes and other aspects of relationships," she added.

Cao said she wanted Lily to understand what sexual harassment was.

In 2001, the Chinese government had proposed to include sex and reproductive health education in the curriculum for compulsory education in a 10-year plan from 2011 to 2020.

Children between the ages of 6 and 14 receive compulsory education in China.

Eight years ago, guidelines on sex education in elementary and middle schools were issued, setting teaching targets for different age groups.

But despite the existing guidelines, students in many elementary and middle schools in China face problems with receiving proper sex education, because either relevant textbooks aren't available or some teachers have yet to be professionally trained for the purpose, according to Fang Gang, a sexologist and professor at Beijing Forestry University.

Last year, Cao organized a three-day summer camp in Chongqing and invited Fang to give lectures as she wanted Lily to get proper sex education.

Over the three days, Lily was joined by 21 other teenagers, all aged 11 and above, in discussions and debates initiated by Fang on a range of issues from relationships to harassment. They were also told about contraceptives and introduced to sexual references in culture through skits.

Although she had basic knowledge about human anatomy, the camp provided Lily a systematic perspective on sex-related issues, she said.

Cao said she was surprised to see how serious all the attending children were when talking about what are generally considered "embarrassing topics" such as masturbation or learning the use of condoms.

"It had a big impact on me when Fang said same-sex relationships are romantic relationships, too, and that homosexuality can't be 'corrected,'" Cao said.

Fang strongly suggested that parents join such courses.

He has delivered the course since 2013 to some 160 children in East China's Anhui province, Chongqing and Xichang, Sichuan province, also in the country's southwest. In August, he will hold classes in Hangzhou in eastern Zhejiang province.

A societal view in China still encourages parents to "manage" the sexual curiosity of their growing children regardless of their need to know more about themselves and on matters of intimacy in personal relationships, which are naturally important aspects of their lives during those years, Fang said.

In June, Yin Shurong from Chongqing, accompanied his 11-year-old son to Fang's class.

"Sex is not mysterious, dirty or embarrassing, and should not be avoided as a topic. It's always there in our lives - like eating or drinking. And children should know about it in a positive, professional way," he said.

The biggest barrier to proper sex education in elementary and middle schools in China is the mindset that sex is a dirty word and children shouldn't be exposed to related discussions, Fang said.

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