During a recent class in Zhangyi, Ningxia Hui autonomous region, teenage girls were having a lively discussion about menstruation, although some hid their faces in their hands or smiled shyly.

On the blackboard at the Zhangyi Middle School was an image of the female reproductive organs with information explaining their functions.

Many Chinese parents prevaricated when it came to answering questions on sex education and reproduction, telling their inquisitive children "We picked you up from a trash can" and "You jumped out of a stone crack" when the youngsters asked where they came from.

In 2010, Yang Xiuhua, the principal of the school, launched an all-girls class to try and address the stigma of talking about physical development, reproduction and health issues. It was designed as a compulsory course for all girls age 14 and older. Each class lasts 40 minutes and has about 60 girls.

Yang teaches adolescent psychology and Nan Yuehong, a biology teacher at the school, has been responsible for the physiology side of the classes for the past 10 years.

"The class is more popular than we thought. While adults usually avoid talking about the issue, students are curious and crave this kind of knowledge despite their shyness in class," said 36-year-old Nan.

Educational material about female sexual organs is limited to an eighth-grade biology book, so Nan also teaches the girls about menstrual hygiene and protecting themselves while contacting with males.

"Students have now become more willing to share their experiences about physical changes in adolescence. They openly discuss things outside of class," Nan said.