Specifically, the investigators looked at teens who had three or more incidents of fighting in school.
Although the levels of teen violence varied by country, overall it decreased in 19 countries including the United States, Lithuania, Germany, Estonia and Great Britain.
In some countries, however, teen fighting increased, including Greece, Ukraine, Spain and Latvia, the researchers found.
Commenting on the study, Dr. Lorena Siqueira, director of adolescent medicine at Miami Children's Hospital, said that one problem is that it doesn't take into account teen violence outside of school or among teens who have dropped out of school.
Data from the U.S. Centers for Disease Control and Prevention (CDC) show that teen violence in the United States had remained pretty steady in the last decade, she said.
"If you look at violence overall it is about one in three kids, but if you look at violence on school property then it drops to the level reported in the study," Siqueira said. "This is a big underestimate."
In a 2011 CDC study of high school youth, 12 percent reported being in a physical fight on school property in the previous year.
Teens who have dropped out of school are at risk for violent behavior, Siqueira said. "The dropout rate can be as high as 20 percent, depending on the neighborhood -- those are the kids who are at highest risk," she said.
Siqueira said she assumed that countries reporting the biggest drop in teen violence are those where economic conditions have improved. "So there is less stress on everybody, and hopefully, less alcohol use," she said.
Children who grow up with violence are more likely to be violent, and poverty increases substance abuse and violence along with it, Siqueira noted. Often community intervention and discussion don't work, she added.
All rights reserved