Bullies with the most hostility reported picking on kids because those kids were not good at sports. The most frequent bullying involved picking on students they perceived to be gay or lesbian, a result that agrees with another recent study on bullying.
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The research seems to indicate bullying is about "social attitudes manifesting themselves in a very basic way within the school environment," said study researcher Ian Rivers of Brunel University in the United Kingdom. "So if the school really upholds sports, kids who are not good at sport are going to be victimized because they are not living up to the expectations of others."

"While [bullies] may well be very sensitive about any differences or any failings that they have, they may also be setting themselves up so that they victimize those who have failings that are more challenged in society, that are perhaps perceived to be more problematic, such as being gay, such as being poor at sports, such as not being good at school work," Rivers told LiveScience.

Both boys and girls were more likely to accept same-gender classmates than other-gender classmates. And boys were more often nominated than girls as perpetrators of bullying toward both boys and girls.

"They aren't interested in the opinion to the whole classroom, only those in their in-group," Veenstra told LiveScience. "In elementary school the in-group is often people from the same sex. Boys are interested in the opinion of other boys in whether they choose the right target or not, and girls are interested in what other girls think."

Bullies tended to target same-gender individuals who were rejected by and had low acceptance from their same-gender classmates. So when boys bully boys, it didn't matter whether girls approved or disapproved. The same went for girl bullies.

In that way the bullies could gain status by dominating other kids while also stay in the good graces of the in-group.

When they did taunt girls, boys chose victims who weren't well-liked by other boys, regardless of the victim's status among girls. Girls did the same in their bullying of boys. But there was one caveat. While male bullies were never rated low on acceptance by male or female peers, when girls bullied boys they were more rejected by both genders. The researchers aren't sure the reason for the gender difference.

"Bullies go for admiration, for status, for dominance," Veenstra said. Unlike friendly teasing, he said, bullying is long-term, unwanted and doesn't occur between social equals.

Despite their aggressive behavior, bullies also want affection, Veenstra said. His work has shown that bullies care about the approval of their own in-group, so they strategically pick victims they know few other classmates will defend.

Other researchers have found evidence that kids who are already socially awkward are more vulnerable to bullies.

"There's actually no good reason," said Young Shin Kim, a professor at the Child Study Center at the Yale School of Medicine. "One day, they just don't like a kid because that kid will wear pink, and the next day they might not like other kids because they're wearing blue, or they're tall, or they're small, or they wear glasses…
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For some kids, bullying behavior is just the tip of the iceberg, Kim said. These children have other problems with aggression and control and may be abuse victims themselves. But there are also many otherwise well-adjusted children who just "think it's a cool thing to do," she said.

Indeed, 85 percent of bullying cases happen for the benefit of an audience, Veenstra said. Bullies want their behavior to be noticed. That means the reactions of bystanders is another essential piece of the bullying puzzle.

"There are often defenders to the victims, but there are certainly more bystanders," Veenstra said. Other children have a difficult time intervening without the support of teachers and authority figures, who are sometimes too quick to dismiss bullying. And adults don't always set good examples. Take driving: Grown-ups often tailgate slow drivers in an effort to intimidate them, Kim said. That's a page right out of the bully handbook.