(CNN) -- Nothing like timing.
Just as I was sitting down to write a story on what we've learned from 40 years of research on bullying, comes news that bullying -- at least at school -- may be on the decline.
The U.S. Department of Education is hailing what it calls the "first significant decrease" in school-based bullying since the federal government started gathering such data back in 2005.
About 22% of students ages 12 to 18 reported they were bullied at school during the school year in 2013. That's down from a range of 28% to 32% of students who reported being bullied at school in previous surveys dating back to 2005, according to data from the Education Department's National Center for Education Statistics.
While any decline is certainly welcome news for students, parents, educators and administrators, the 22% figure still means that more than 2 of every 10 students are being bullied at school. And those numbers don't include kids who don't report the bullying, or students who are being bullied away from school grounds.
What can we do to bring those numbers to zero, or as close to zero as we can get?
That's the thinking behind an ambitious undertaking by two prominent researchers on bullying. Inspired by the White House Conference on Bullying in 2011, the researchers set out to analyze four decades of data on bullying to figure out what we know and how that knowledge can be used to implement programs to prevent bullying and keep our kids safe.
"We felt like within the bullying space there were a lot of myths and misconceptions, and things that we know as researchers that somehow seemed to get lost in translation," said Susan Swearer, co-author of the comprehensive review of bullying research (PDF), which was published in a special issue of American Psychologist, the official journal of the American Psychological Association.
Among those myths: Bullies must come from horrible homes (not true), bullies are unpopular and anti-social (not always the case), and bullying is only an issue between one perpetrator and one victim (not usually true), said Swearer, who is co-director of the Bullying Research Network and professor of school psychology at the University of Nebraska.
So CNN wanted to glean what we actually know about bullying -- its causes and effects -- from actual research, not from conventional wisdom, social media ramblings or popular culture.
Here are 10 things we know based on 40 years of research, according to Swearer and co-author Shelley Hymel, professor of human development, learning and culture at the University of British Columbia.
1. Bullying can impact mental health
Involvement in bullying -- whether as a victim, a perpetrator or even a bystander -- can lead to depression, anxiety and feelings of hopelessness, said Swearer, pointing to studies that have been done in the United States and other countries.
In fact, a recent study reported by CNN found that adolescents who are bullied by their peers face worse mental health effects into adulthood than children who are maltreated by adults.
Bystanders to bullying can also be affected, said Swearer. They may not want to go to school because they feel unsafe and worry they could be the next target. They may also suffer feelings of hopelessness, thinking there's nothing they can do about the bullying, she said.
2. A kid can bully and be a victim, too
Swearer said based on more recent research, we also know that kids can function in multiple roles.
"They can bully somebody in one setting and they can be bullied in another setting, and so these aren't just fixed separate roles."
Knowing kids can occupy both these bully and victim roles is critical to intervention, she said.
"I will never forget one kid (who) said to me, 'I got in trouble for bullying and I realize that was wrong, but I feel angry that the school doesn't realize that I'm being bullied, too,' " said Swearer.
3. The influence of peers
It's extremely rare to have bullying unfold where you just have "this horrible bully and the completely victimized kid and nobody else is around," said Swearer.
Usually, it occurs in the presence of peers, who play a critical role in maintaining or snuffing out the bullying behaviors.
"Peers really influence the climate and the ability of bullying to kind of take place," she said. "So within the peer culture is this seen as something that this is just what people do?' "
4. Bullies can be the popular kids
There are "highly socially skilled kids" who engage in bullying behaviors, said Swearer.
"In some sense, it kind of makes sense to think about if you're going to bully somebody and get away with it, you've got to be pretty socially savvy to figure out, 'OK, who can I pick on and not get caught?' "
And if bystander kids see that bullying is a way to win popularity and achieve a high social status among their peers, they may do it themselves, she said.
5. Bullying can occur in real and virtual space simultaneously
There have always been different forms of bullying -- verbal, relational and physical -- but in the Internet age, we can now add the digital world to the mix.
What we know from all the research is that these different forms of bullying tend to "co-occur," said Swearer.
A bully's mindset might be, " 'I'm going to physically bully somebody while I'm going to verbally bully them as well and then maybe I'll take a picture of it and send it around on my SnapChat,' " she said.
6. Both boys and girls bully
Many people might think that boys bully more than girls, but based on the research, there are not a lot of gender differences, said Swearer.
Some research has shown that boys engage in more physical bullying than girls, she said, but other studies suggest that girls engage in more verbal, relational and cyberbullying than boys.
More research is needed, said Swearer. "We still have more to do in terms of some of the precision with which we look at these different forms and then look across gender and then age as well."
7. Bullying increases during transition times
Most of the research shows that middle school tends to be "peak years" for bullying, although it can occur as young as in preschool and later into adulthood.
"There are people who are seeing bullying in retirement communities, so it's not necessarily something that someone could 'outgrow,' " Swearer said.
Bullying is particularly "salient" during transition times for kids, such as graduating from elementary to middle school or again on to high school -- times when kids are actively "negotiating" new peer groups and figuring out where they fit in.
8. Many kids don't tell on bullies
While schools tout their zero-tolerance polices when it comes to bullying and encourage students to report it, many kids won't do so.
"They worry that it's not going to ... (change) anything," said Swearer. "And then they worry, 'Is there going to be retaliation?' And so they just don't really have the confidence that the school is going to handle it."
Swearer also said there are plenty of anecdotal examples where a student who reported being bullied and the alleged bully both end up getting punishments. "So I think that communicates, 'Well, that wasn't that effective.' "
9. Serial bullies responsible for most of the bullying
In any given school, let's say 40 kids say they have been victimized by a bully. Rarely would there be a case where the school has 40 different bullies on its hands.
"It's typically a pretty small handful of the kids who are continually perpetrating bullying behavior," said Swearer. So-called "serial bullies" accounted for nearly 70% of victim reports, according to some research.
"If we can ... take those handful of kids and actually really treat them, then if they in turn learn more positive ways of interacting and ... we wouldn't have the bullying."
10. There's no profile of a bully
Based on four decades of research, we also know that there is not a "consistent kind of profile" of a child who might be bullying others, said Swearer.
There are multiple individual and family characteristics that could play a role, from impulsivity to low self-esteem to troubles at home, she said. But other influences -- such as a student's peer group -- could be a factor as well.
Swearer's research includes working with kids who bully others to figure out why they do.
When people hear what she does, often someone will say, "Well, what are they like?" she said.
"And I'm like, they're a kid ... They're not like some scary kid. It's just a kid. So I think that that's kind of a myth too. This idea that somehow a kid who bullies is the scary kid. More often than not, they're just a kid and they've made some poor choices."
What's needed to stop bullying?
After analyzing 40 years of research, Swearer says she's more convinced than ever of the need for mental-health services, such as counseling, at schools.
"I really see that that is the missing piece," she said. "So many families and kids ... can't access mental health treatments and so they either don't know where to go or they don't have the means. They don't have the transportation.
"And so to me, one of the solutions is bolstering school-based mental health resources. I think that that's one of the keys to reducing bullying among kids."
Do you think bullying is on the decline? Share your thoughts with Kelly Wallace on Twitter @kellywallacetv or CNN Parents on Facebook.
Editor's note: Kelly Wallace is CNN's digital correspondent and editor-at-large covering family, career and life. Read her other columns and follow her reports at CNN Parents and on Twitter.
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