One student held up a poster that read, "We only live once, why marry early?" referring to a common situation in which young couples are forced to wed because of unwanted pregnancies.
Sumarsono, head of reproductive health at the women's and social empowerment agency in Yogyakarta, responded that there were already too many subjects in school.
"Due to the limitations in the curriculum, our effort now is to make sex education an extracurricular activity," he said.
The meeting was part of a larger effort to push for legislation that would make sex education a mandatory part of Indonesia's national curriculum. Yogyakarta, a university town known for its vibrant student and cultural life, has been at the forefront of Indonesia's sexual education revolution.
"We're trying to ensure information reaches a broader audience," said Andreas Nugahita, 13, who attended the meeting. "The more people understand, the more they can take responsibility for their own sexual behavior. That could change teenagers' attitudes toward sex all across Indonesia."
Andreas is one of hundreds of students who have been trained as peer educators by Planned Parenthood in Yogyakarta, a province with one of the country's most progressive reproductive rights communities. The hope is that they will pass along information about HIV/AIDS, contraception and sexual orientation to their classmates, most of whom learn about sex through the Internet.
"Here, sex is considered taboo, and as a result talk about sex is filled with myths," said Mariana Amiruddin, executive director of Jurnal Perempuan, or Women's Journal.
Jurnal Perempuan is one of three private organizations forming the Sexual and Reproductive Health and Rights Task Force, which has drafted a sex education curriculum that is to be tested in the coming months. Selected schools in 10 districts across Indonesia's vast archipelago will be part of the project.
"People need to know that the lack of knowledge is really bringing youth down," said Dyana Savina Hutadjulu, a program officer for sexual and reproductive rights at Hivos, a global development agency helping to coordinate the effort. "We have this conservative point of view because, for generations, sex has been seen as a bad thing."
Hutadjulu said the effort to make sex education mandatory was an uphill battle.
Sex education advocates were initially encouraged when Dr. Nafsiah Mboi, a physician who has promoted youth outreach and condom use, was appointed as Indonesia's health minister in June.
According to a 2011 survey by the Health Ministry, only 20 percent of Indonesians ages 15 to 24 had comprehensive knowledge of HIV, a figure that Nafsiah said required a dramatic improvement.
"I believe in reaching out to youth - I do believe they have the right to information," she said in an interview after a media briefing by the U.N. AIDS agency in October. Nafsiah, however, stepped back from her support for sex education after her campaign to promote condom use among groups at risk of contracting HIV provoked a public backlash last year.
This back-and-forth is indicative of the wider effort to promote sex education. In Indonesia, many conservative officials feel that sexual topics are too sensitive to be discussed publicly and oppose mandatory sex education. Groups like the Indonesian Council of Ulema are also influential in the majority-Muslim country.
"Students don't need to be taught about sexuality - they can do that on their own," Ma'ruf Amin, chairman of the Indonesian Council of Ulema, said in an interview last year. "What they need to know is about limitations, so they will know not to have sex before marriage."
Maesur Zaky, director of Planned Parenthood in Yogyakarta, said the mayor of Kulon Progo was pushing for sex education to be compulsory, which would make it the first district in Indonesia to do so. The mayor had backed a decree to allow schools to integrate sex education in the curriculum, but had run into resistance from the local department of education.
"There must be a better understanding about reproductive health," said the mayor, Hastro Wardoyo. "It would be better if it became a part of the curriculum, but what's important is that the substance is taught to the students."
Sri Mulatsih, head of the local department of education, said the curriculum had to be tested first. "We dare not launch the program without making sure it's suitable. That would be dangerous," she said.
"It's a tricky issue," said Mr. Zaky, who explained that officials did not want to be seen as promoting promiscuity by advocating protected sex among youths. "They don't want to be judged as immoral."
Still, advocates are making some headway in getting sex education into schools.
Planned Parenthood in Yogyakarta has been providing sex education since 2008. More than 50 schools in Yogyakarta province have agreed to start using the organization's curriculum, which includes lessons about contraception and sexually transmitted diseases. The Yogyakarta curriculum has been used a loose model for the proposed national one.
Last year, Planned Parenthood in Yogyakarta started holding workshops to help parents discuss protected sex with their children.
"We don't talk about this with our parents," said Farah Suhailah, 15, a Planned Parenthood peer educator. "And if teachers talk about it, they feel uncomfortable."
Reproductive rights advocates warn that low awareness about sex and sexuality is fueling a rise in cases of HIV, unwanted pregnancy, early marriage and unsafe abortions.
"The way we convince teachers to be brave and sensitive is by showing them the facts," Zaky said.
A study last year by the Health Ministry found that 42 percent of patients with HIV/AIDS in Indonesia were 20 to 29. A survey commissioned by international health organizations in 2011 for World Contraception Day showed that nearly half of Indonesians surveyed had a close friend or family member who had an unplanned pregnancy in recent years, more than Thailand, India or China.
Michelle Bachelet, executive director of U.N. Women, who visited Jakarta in December to attend meetings about women's rights, said at the time, "If we see the facts, we see that young people are starting their sexual life very young, with no information, and making bad choices."
Inna Hudaya, director of Samsara, a Yogyakarta-based organization that provides counseling and advice, mostly to girls and women, about safer sex and abortion, said talking about unwanted pregnancy opened the door to discussions of other issues.
"Many youths know how to have sex, but they don't know the consequences," she said.
Samsara has a sexuality and reproductive health school that hosts village-level workshops where they talk about body image and teach women how to perform self-exams for breast cancer.
"Sex education is not just about biology," said Zoya Amirin, an Indonesian sexologist who is writing a book to dispel common myths about sex. "It might teach you about reproduction, but it doesn't teach you how to say no to premarital sex, how to tell your boyfriend or girlfriend, 'I think I need to wait for sex until I'm ready."'