“THEY forced my ten-year-old son to wear used toilet paper on his head,” complained a mother in Beijing on WeChat, a Chinese social-media site, in 2016. Her post soon went viral. It touched a nerve in a country where school bullying has traditionally been seen as a rite of passage. Her son’s school, one of the best in Beijing, dismissed the brouhaha as “harmless mischief between kids”. But a spate of reports about even more vicious acts of bullying at other schools soon followed.

Officials reacted swiftly, passing anti-bullying legislation at both national and local levels. So today China’s anti-bullying policies are among the world’s toughest. In one Beijing district staff at public schools are required to report incidents of bullying to the local education authority within ten minutes of observing them. (How to punish the bullies is yet to be worked out.)

Surveys in Britain and America consistently show that the biggest worry parents have for their school-age children is that they will be bullied. In Japan more pupils commit suicide on September 1st, just before the start of the new term, than on any other day. But educators struggle to spot bullying, let alone to stop it. Many victims are too ashamed to tell a teacher. One former victim who recently finished high school in Vancouver says he kept the pain to himself for several months, worried that teachers would “judge” him.

Globally, bullying tends to peak in the early-teenage years before tapering off. Boys are slightly more likely than girls to engage in it, and to bully both sexes. Girls tend to bully other girls. Boys are more likely to use their hands and feet. Female tormentors prefer “relational” bullying, such as spreading false rumours or exclusion from a social group.

Children who are from ethnic minorities, short, obese, disabled, gay or have poor social skills are at higher risk. Victims of bullying may in turn bully others. In America bullies pick on “nerds”. In China and South Korea, by contrast, those with poor grades are at higher risk. A study in 2013 of the Arab world found that the best predictor of being bullied was having crooked teeth. But bullied children everywhere risk long-term health effects. A graduate student at Oxford University says he was “emotionally scarred for at least five years” after being tormented in middle school in Hong Kong.

The prevalence of bullying varies greatly across the world. Data, largely based on students’ own reports, probably underestimate the scale of the problem. They suggest bullying is most common in parts of Africa. A survey from 2011 found that 70% of Egyptian 13- to 15-year-olds reported being bullied at least once in the past 30 days. At the other end of the spectrum stands Sweden, where, according to a poll from 2014, only 11% of children in the same age group reported being bullied in the past month. In America, Britain and Canada the rate is between a quarter and a third. Cross-country comparisons, however, are problematic. Perceptions of what constitutes bullying vary across borders. For instance, the Chinese word for bullying, qifu, has a very physical connotation.

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Most rich countries have anti-bullying laws. In Britain all state schools have since 2006 been required to adopt a school-wide anti-bullying policy. By 2015 every state in America had anti-bullying legislation. States with the strictest laws, such as Massachusetts, require school officials to report all bullying to the head, who must “promptly conduct an investigation”.

Central to tackling bullying in schools, argues Christina Salmivalli of the University of Turku in Finland, is to encourage bystanders to intervene. The main motivation for bullying is the drive for social status. By teaching bystanders to speak up, or at least not to laugh at the victim, the “social rewards” of bullying can be reduced, she says. In the late 2000s Ms Salmivalli formulated an anti-bullying programme called KiVa (the Finnish word for “nice”), which includes team-building exercises and online simulations. Today it is taught in thousands of schools in Finland, and hundreds more around the world, with promising results. Most surveys of KiVa’s effects show steep drops in the numbers reporting themselves bullied.

Other approaches abound. Many school-bus drivers in North America assign seats, keeping suspected bullies close to the front. Every classroom at Rhiw-Bechan School in mid-Wales has a “worry-box” for pupils to report bullies anonymously.

Anthony Parker, head of Weston High School in Massachusetts, says he informs parents any time their child is accused of bullying. Nine times out of ten, the bullying then stops. An anti-bullying bill proposed in March in Pennsylvania would allow a judge to mandate community service or levy a $500-750 fine on parents if their child is caught bullying, starting from the third offence.

Some approaches have been shown to backfire. “Restorative” methods that put the bully and victim together to patch things up may end up further traumatising the victim. Some sorts of punishment, like expulsion from school, may simply shift the problem elsewhere.

Cultural differences complicate the picture. In China, for example, rural migrant workers in cities are treated as second-class citizens. Their children, when bullied, may attract less sympathy from teachers. Such unfairness helps explain why, distressingly, some victims will always decide that the only answer to bullying is to fight fire with fire. One such, Alexander, a 23-year-old now working in Canada who spent part of his childhood in Uzbekistan, says that “sometimes you have no choice but to match the aggressiveness of the bully. It worked for me.”

Correction (October 17th 2018): This article previously stated that the International School of Beijing has security guards in every changing room. The school tells us this is no longer the case. The policy, which was introduced to deter theft, has been discontinued. The reference has been removed.