Sex education is common in Western schools but these ground-breaking lessons are taking place in deeply conservative rural Pakistan, a Muslim nation of 180 million people.
In neat rows, the Pakistani girls in white headscarves listened carefully as the teacher described the changes in their bodies. When the teacher asked what they should do if a stranger touched them, the class erupted.
"Scream!" one called out.
"Bite!" another suggested.
"Scratch really hard with your nails!" a third said.
Publicly talking about sex in Pakistan is taboo and can even be a death sentence. Almost nowhere in Pakistan offers any kind of organised sex education. In some places it has been banned.
But teachers operating in the village of Johi in poverty-stricken Sindh province say most families there support their sex education project.
Around 700 girls are enrolled in eight local schools run by the Village Shadabad Organisation. Their sex education lessons - starting at age eight - cover changes in their bodies, what their rights are and how to protect themselves.
Three girls cram into each seat made for two, listening attentively to teacher Sarah Baloch. One flashcard shows a girl stopping an old man from touching her leg. Other cards encourage girls to tell their parents or friends if someone is stalking them.
The girls are shy but the lessons have sunk in.
Teachers display a card with an illustration depicting a girl going through a medical checkup by a doctor, as they describe preventive measures to avoid when sexual harassment occurs.
The lessons even teach the girls about marital rape - a revolutionary idea in Pakistan, where forcing a spouse to have sex is not a crime.
Tahir Ashrafi, who heads an alliance of moderate clerics called the Pakistan Ulema Council, said such lessons were permissible under Islamic law as long as they were segregated and confined to theory.
"If the teachers are female, they can give such information to girls in the limits of Shariah," he said.