Anyone who has been near a middle school in recent years has heard of efforts to stop students from bullying: A special school assembly, say, or a letter warning parents to watch for vicious attacks on social media.

Princeton University researcher Betsy Levy Paluck and her colleagues took a more direct approach to reduce this age-old type of conflict. They got popular and influential students to take a stand against it.

The results of Paluck's 2016 study, conducted in 56 middle schools across New Jersey, helped to place her in an elite group this week. She is among 24 winners of this year's MacArthur Fellowships, the coveted awards informally referred to as "genius" grants.

Paluck, 39, a professor of psychology and public affairs at Princeton, said she was stunned by the news and felt the award should be shared among many who have helped her. She also was recognized for her studies of ethnic tolerance in Rwanda and of attitudes toward same-sex marriage.

"This is a real team sport," she said of her research. "You need a lot of hands to get this work done."

Other winners included artists, historians, scientists, and writers, chosen by a secret selection committee from a pool of confidential nominees. Each receives $625,000 from the Chicago-based MacArthur Foundation, spread out over five years to spend as they like.

Like most winners, Paluck had no idea she was under consideration, and learned of the honor several weeks ago via phone. The caller, whose name Paluck did not recognize, asked if she could speak confidentially.

Vaguely alarmed, the psychologist shooed all the graduate students out of her office.

"I thought something was wrong," Paluck said.

Elated to learn otherwise, she was sworn to secrecy until the awards were announced Wednesday.

On the bullying study, published in January 2016 in Proceedings of the National Academy of Sciences, Paluck collaborated with Hana Shepherd of Rutgers University and Peter M. Aronow of Yale.

The researchers conducted the experiment with the same rigor that one would use for testing a new drug, randomly selecting half of the 56 schools to participate during the 2012-13 school year.

Students were asked to list peers with whom they had spent time in the last few weeks. From those lists, the researchers calculated which students held the most sway among the student body. These were not necessarily the most popular, but they all were "social referents" — those whose behavior was most likely to be observed.

The researchers then randomly selected participants within the schools — including students who were influential and those who were not — and pulled them out for special sessions where they identified types of conflict at the school and devised campaigns to oppose it. Some decided to give out wristbands as rewards for promoting tolerance, while others spread anti-bullying messages on social media. The key was letting the students, an average of two dozen in each school, take the lead, Paluck said.

"We didn't give them a manual written by adults telling young people, 'Just say no to bullying,' or telling them what to say at all," she said.

The authors found that incidents of peer conflict, as measured by disciplinary records, were 30 percent lower in schools where students were taking a stand against conflict, compared with the schools in which there was no intervention. That was an average figure; the drop in peer conflict was as high as 60 percent in schools where more of the participants held influence in the student body.

Psychologist Stuart Green, director of the New Jersey Coalition for Bullying Awareness and Prevention, said that bullying remains all too prevalent in schools but that Paluck's research was valuable.

"I'm a fan of the work," he said. "It offers a useful understanding of approaches to improving school climate and addressing peer conflict."

Paluck agreed that bullying remains pervasive. The key is to enlist influential students in shaping what is perceived as "normal and desirable," she said.

"While we all have an influence on our peers," she said, "some people have an outsize influence."