Sex education is a highly controversial topic in traditional Indian society.
In a Delhi classroom, 40 sheepish girls and boys stare silently at a sketch of a couple making love.
The sex education lesson for 15-year-olds is not part of India's national syllabus, and the exclusive private school teaching the subject is taking a risk by passing on the facts of life to its pupils.
Traditionalists say such classes are against Hindu sensibilities and invade a private matter that is best dealt with inside the family home.
But, with rapid social change in India, calls for teenagers to be taught about human reproduction and sexual health are growing, and private schools across the country now give discreet lessons to their privileged pupils.
"India allows teenagers to learn English and other European languages, devour pizza, burgers, wear skimpy clothes, and dance to English music," teacher Rubina Hussain Sheikh told her class.
"These Western influences are welcomed. So why is talking about sex in schools not accepted?"
Sheikh, a counsellor whose lesson communicates sexual information in a simple and relaxed manner, admits it is a "tricky subject", but she believes it is a vital duty to combat ignorance.
She displays slides from the ancient Indian erotic text Kamasutra, as well as drawings of how an adolescent's body develops, and graphics to explain AIDS and the rise of sexually-transmitted diseases in India.
Students at the school often hesitate to ask questions, she said, but they all feel the course helps clear away many of the misconceptions and the secrecy that shrouds such taboo subject.
"I had no clue about sex, pregnancy and the precautions required to protect oneself during an intercourse. I am glad that I am aware now," said Riddhima Tiwari, a 15-year-old student at the school, which asked not to be named to avoid publicity.
Parents said they had permitted the course to be taught as they were aware their children needed to be able to look after themselves, adding it would pass on information which they would be shy of discussing at home.
But millions of students studying in government schools are denied any such advice, as India state governments avoid all mention of introducing sex education in schools.
"If implemented, the subject would have adverse effects on young minds," said Swami Nityanand, a Hindu priest in Delhi and a senior member of the right wing Hindu organisation, Vishwa Hindu Parishad.
Nityanand said he never uses the word "sex" in front of his young disciples, as he feels that Indians learn all the facts of life naturally and need no guidelines on the topic or diseases related to it.
In 2007, Nityanand's followers burnt school books that discussed contraception and sexually-transmitted diseases, and forced the government in the western state of Gujarat to drop reproduction chapters from science textbooks.
"Imparting this kind of education would mean devaluing Indian culture and values, so I will fight until the end to protect our rich heritage," he told AFP.
But a 2007 survey "Indian Adolescent: Changing Sexual Behaviour", conducted by doctors and voluntary organisations, concluded that there was an urgent need for sex education in schools.
It said around 40 per cent of all HIV infections in India occurred in the 16-24 age group and clinic-based evidence suggests that a third of all abortions may take place among unmarried teenage girls.
Teen pregnancy also doubled in the previous five years, the survey stated.
And, according to the National Crime Records Bureau, more than 20,000 rapes are reported every year, of which 25 percent of the victims are minors.
Many experts blame such an array of statistics on the lack of sex education.
"This theory of Indian culture and morality is a big sham," said Ravi Kumar Tandon, a Delhi-based doctor who specialises in sexual issues.
"Girls and boys need to learn about sex, and boys have to be trained to adopt alternative modes of relating to women, rather than just being aggressive," he said.
Tandon collected data for the "Indian Adolescent" survey by interviewing about 500 urban and rural teenagers.
"There are misconceptions galore in their minds. Many rural girls thought a man's touch was enough to make a them pregnant, while the urban boys said they access the Internet and watch pornographic videos to understand sex," he said.
He said conservative groups were being hypocritical and unrealistic about the problems of modern India.
"To educate the youth about sex, and to show them how to use a condom will not westernise them. It will make them aware of their sexuality," he said.
However, India's central government appears less than keen to discuss the subject.
"What can I say about sex education? We are yet to apply our mind over the issue," Human Resource Development minister Kapil Sibal told AFP.