"You're seeing more problems like violence, bullying, and even extraordinary issues like the homeless population, that are all impacting our schools," he said. "With increases in poverty, you get changes in the school-age population, but you also don't have the businesses to support a school and you also don't have the community fabric that's needed for a school to succeed."

Abby Beytin, president of the Teachers Association of Baltimore County, pointed out that in both gun-related incidents, teachers or staffers intervened to prevent more violence.

At Stemmers Run, a female teacher "grappled" with the student holding the gun until he dropped it, said officials, who did not identify the teacher or student. At Perry Hall High, 15-year-old Robert Gladden Jr. was wrestled to the ground by guidance counselor Jesse Wasmer, and got off just two rounds, one of which hit 17-year-old Daniel Borowy, according to police.

But Beytin said that even when teachers sense "red flags," they are not always trained on what to do next.

"Teachers in particular are concerned about not having the tools necessary," she said. "I think they're clamoring for ways to get more information."

Acting bravely at a moment's notice and properly assessing risk ahead of time are two separate things — and teachers aren't trained for the latter, McGee said. "Trying to get educators to do violence risk assessment is like trying to get a cop off the streets and [into] a classroom to teach U.S. history."

McGee said Baltimore County should create "a multidisciplinary threat assessment committee, so when the English teacher gets a kid's diary and it has suicidal thoughts and references to Columbine and things like that, they don't try to assess it themselves. That committee should determine if there is enough information about this kid to warrant an assessment, and then when they've made that decision, they punt it to someone who actually has a background in violence risk assessment."

McGee said that before the Virginia Tech massacre in 2007 the English department faculty and school administrators had noticed the shooter's troubling behavior. Yet the student never received the professional help he needed.

"Imagine if [the university's] heating and air conditioning failed, and they got their English faculty and school administration to fix it," McGee said. "No. You'd call in the pros."

Newman said her research has also shown that police officers stationed in schools play an important role in encouraging students to come forward with troubling information. Students "were more likely to come forward to them than they were to school authorities. They see them as more independent and as people with investigative resources or skills."

Baltimore County has about 60 school resource officers. Each high school has from one to three officers, according to the Police Department. And all but five of the county's middle schools have an officer.

Still, Newman cautioned against eyeing specific students for potential violence, because it is extremely difficult to create a "profile" of likely shooters.

"Generalizing from very rare events is always risky," Newman said. "We don't know what kinds of circumstances produce shooters; we can't predict where they come from. … It's a false comfort to think we could figure out in advance what sort of person does this."

The FBI offers a similar caveat in its report, "The School Shooter: A Threat Assessment Perspective," which provides a model for evaluating school-based threats.

"This model is not a 'profile' of the school shooter or a checklist of danger signs pointing to the next adolescent who will bring lethal violence to a school. Those things do not exist," the report says.

The FBI report nevertheless lists a range of behaviors that should be carefully reviewed if a student is perceived to have made a real or veiled threat of violence. Among them: poor coping skills, depression, narcissism, anger, inappropriate humor, dehumanizing others, and externalizing blame.

Newman said her research shows school shooters are "very often trying to correct what they perceive is a damaged reputation as a loser among peers" and often verbalize their intentions to do something dramatic or violent.

Sometimes, they promise such actions so much that they eventually become teased for not carrying through, she said. "By that time, they feel that they've painted themselves into a corner, and they feel that they have to do what they've been saying they are going to do."

Baltimore Sun reporter Erica L. Green contributed to this article.