What do Bolivia, Belgium, Burkina Faso, China, the Democratic Republic of Congo, Ecuador, Egypt, India, Kenya, Malawi, Nigeria, Scotland, South Africa, the United States and Vietnam all have in common?

The pervasive idea is that girls are vulnerable and that boys are strong and independent.

In a set of studies published Wednesday in the Journal of Adolescent Health, the researchers concluded that between the ages of 10 and 14, children begin to fully embrace and internalize the belief that girls and boys are intrinsically different — and should act accordingly.

A 12-year-old girl in Delhi, for example, told researchers she understood that "when [girls] are small they can wear any clothes, but as girls grow up they have to wear covered clothes, talk in a certain manner." In Shanghai, parents and kids said in interviews that girls are meant to act gentle and quiet, whereas boys should be brave, strong and tough. And a 13-year-old boy in Baltimore explained that fathers aren't as protective of their sons as their daughters, because a son is raised to "to be a man" whereas a daughter will always be a "little princess."

"The health consequences of these gender norms are huge," says Robert Blum, a pediatrician and professor of public health at Johns Hopkins University who led the study. When boys and men are taught that girls are weak, sexual objects for the taking, "adolescent girls pay a vast price," Blum says. "They are at greater risk for HIV and STIs, child marriage, they are at far, far, far more risk of gender-based violence."

For boys, an emphasis on being strong — or macho — encourages them to engage in risky behavior like smoking, drinking and using drugs at an earlier age. They're also more likely to get injured in traffic accidents and die of homicide, Blum says. "To believe that some are beneficiaries and some are victims is absolutely wrong — everyone is a victim of these gender norms."

None of the findings surprisedAnju Malhotra, who leads the gender and development program at UNICEF. "This kind of study is very important to lay the groundwork," to change gender norms, she says. "But we need to quickly go beyond that and invest in policy and programs."

For Malhotra this includes working with governments to improve girls' access to education and jobs through scholarships and affirmative action schemes. UNICEF's Gender Action Plan — which Malhotra oversees — also highlights the importance of improving women's access to health care. These are simple, obvious steps, she says, but the only real way to change gender norms are through laws and policies that empower girls and women.

Blum agrees — and points out that policy changes over the past few decades have already helped change certain social norms. "In 1980 there weren't really laws against rape within marriage," he says. "Today in many places it is criminal."

But he says policy isn't enough. "The first step is to work with young people," he says, "and give them the opportunity to consider different ways of thinking about gender."

To that end, groups like Promundo in Brazil and GREAT in Uganda encourage boys and girls, as well as their parents and teachers, to question gender stereotypes through workshops and seminars.

In Serbia, the nonprofit Center E8 offers teenage boys a couple of days off from school if they agree to attend a workshop on gender.

That's what roped in 19-year-old Djordje Aleksandrovic. He first attended such a seminar four years ago.

"By the end of that first seminar, I really started to question a lot of things," Aleksandrovic says, like the idea that there was something weird or wrong about being gay. And after learning about workplace discrimination and sexual harassment, he "realized that on paper [women] have equal rights — but it's not like that in real life."

"These were topics that were never discussed," he says, either at home or in school. "And at first I maybe didn't agree with everything that they said."

But then, "it made me see other side of the story," he says. "And I saw not everything is black and white."

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