(CNN) Bullying can be defined by many things. It's teasing, name-calling, stereotyping, fighting, exclusion, spreading rumors, public shaming and aggressive intimidation. It can be in person and online. But it can no longer be considered a rite of passage that strengthens character, new research suggests.

Adolescents who are bullied by their peers actually suffer from worse long-term mental health effects than children who are maltreated by adults, based on a study published last week in The Lancet Psychiatry.

The findings were a surprise to Dr. Dieter Wolke and his team that led the study, who expected the two groups to be similarly affected. However, because children tend to spend more time with their peers, it stands to reason that if they have negative relationships with one another, the effects could be severe and long-lasting, he said. They also found that children maltreated by adults were more likely to be bullied.

The researchers discovered that children who were bullied are more likely to suffer anxiety, depression and consider self-harm and suicide later in life.

While all children face conflict, disagreements between friends can usually be resolved in some way. But the repetitive nature of bullying is what can cause such harm, Wolke said.

"Bullying is comparable to a scenario for a caged animal," he said. "The classroom is a place where you're with people you didn't choose to be with, and you can't escape them if something negative happens."

Children can internalize the harmful effects of bullying, which creates stress-related issues such as anxiety and depression, or they can externalize it by turning from a victim to a bully themselves. Either way, the result has a painful impact.

The study also concluded with a call to action, suggesting that while the government has justifiably focused on addressing maltreatment and abuse in the home, they should also consider bullying as a serious problem that requires schools, health services and communities to prevent, respond to or stop this abusive culture from forming.

"It's a community problem," Wolke said. "Physicians don't ask about bullying. Health professionals, educators and legislation could provide parents with medical and social resources. We all need to be trained to ask about peer relationships."

Stopping bullying in schools

Division and misunderstanding are some of the motivations behind bullying because they highlight differences. If children don't understand those differences, they can form negative associations, said Johanna Eager, director for the Human Rights Campaign Foundation's Welcoming Schools program.

Programs such as Welcoming Schools , for kindergarten through fifth grade, and Not in Our School , a movement for kindergarten through high school, want to help teachers, parents and children to stop a culture of bullying from taking hold in a school or community.

They offer lesson plans, staff training and speakers for schools, as well as events for parents.

Welcoming Schools is focused on helping children embrace diversity and overcome stereotypes at a young age. It's the best place to start to prevent damaging habits that could turn into bullying by middle school or high school.

The lesson plans aim to help teachers and students by encouraging that our differences are positive aspects rather than negatives, whether it be in appearance, gender or religion, Eager said. They are also designed to help teachers lead discussions and answer tough questions that might come up.

Teachable moments present themselves in these classrooms daily, and Welcoming Schools offers resources to navigate those difficult moments. If they are prepared, teachers can address it and following up with a question.

They cover questions from "Why do you think it's wrong for a boy to wear pink?" and "What does it mean to be gay or lesbian?" to "Would you be an ally or a bystander if someone was picking on your friend?" and "Why does it hurt when someone says this?"

Welcoming Schools is present in more than 30 states, working with about 500 schools and 115 districts.

Not in Our School has the same mission to create identity-safe school climates that encourage acceptance. They want to help build empathy in students and encourage them to become "upstanders" rather than bystanders.

Their lesson plans and videos, viewed by schools across the country, include teaching students about how to safely intervene in a situation, reach out to a trusted adult, befriend a bullied child or be an activist against bullying. While the role of teachers, counselors and resource officers will always be important, peer-to-peer relationships make a big difference, said Becki Cohn-Vargas, director of Not in Our Schools.

These positive practices can help build self-esteem and don't focus on punishing bullies because the emphasis is on restorative justice: repairing harm and helping children and teens to change their aggressive behavior.

But it can't be up to the schools alone.

"What's really important is getting the public and the medical world to recognize bullying for what it is -- a serious issue," Cohn-Vargas said.

A global problem

Bullying, the study suggests, is a global issue. It is particularly prevalent in countries where there are rigid class divisions between higher and lower income families, Wolke said.

Dr. Tracy Vaillancourt, a University of Ottawa professor and Canada Research Chair for Children's Mental Health and Violence Prevention, believes that defining bullying can help in how we address it. Look at it as a behavior that causes harm, rather than normal adolescent behavior, she said.

Role models should also keep a close eye on their own behavior, she said. Sometimes, adults can say or do things in front of their children that mimic aggressive behavior, such gossiping, demeaning others, encouraging their children to hit back or allowing sibling rivalry to escalate into something more harmful.

"We tend to admire power," Vaillancourt said. "But we also tend to abuse power, because we don't talk about achieving power in an appropriate way. Bullying is part of the human condition, but that doesn't make it right. We should be taking care of each other. "

The study compared young adults in the United States and the United Kingdom who were maltreated and bullied in childhood. Data was collected from two separate studies, comparing 4,026 participants from the Avon Longitudinal Study of Parents and Children in the UK and 1,273 participants from the Great Smoky Mountain Study in the U.S.

The UK data looked at maltreatment from the ages of 8 weeks to 8.6 years, bullying at ages 8, 10 and 13 and the mental health effects at age 18. The U.S. study presented data on bullying and maltreatment between the ages of 9 and 16, and the mental health effects from ages 19 to 25.