"If clinicians are going to talk to kids about a variety of issues, one of the issues that kids have to worry about these days is violence," Hemenway said.

He said that if counselors know what factors to look for, they could direct their attention to students who could pose a risk to the school.

"You would want to watch them more carefully," Hemenway said. "If you found out a kid has been in fights, you would want to talk to them about it."

Hayes and Hemenway did not directly study the actual use of guns once they were brought into schools, but it is likely, Hemenway said, that those who carry guns into schools would be the ones likely to use them.

Hayes and Hemenway said that the problem of high school students using firearms has not been properly addressed because of the fact that the factors that they analyze, such as tendency to use drugs or participate in illegal activities, are difficult to quantify exactly.

"I think that what's happened in the last 10 to 15 years is that the public community had become aware of what a serious problem gun violence is," Hemenway said. "Better studies and powerful organizations are pushing for changes. This is just one study, and you need a lot of studies."