(NEW YORK) -- "Weird kid." "Not well." "Hated looking at your eyes."
Those are just a few descriptions of Adam Lanza, the young gunman who killed 20 children and six adults at Sandy Hook Elementary School in Newtown, Conn., last Friday before turning a gun on himself.
While Lanza's mental health remains a topic of speculation, experts say more should be done to flag "weird" and withdrawn behavior that might signal mental illness -- a job that in our education system largely falls to overstretched teachers and school administrators.
"We're the first line of defense, but we're not mental health professionals," said Mel Riddile, a former principal and associate director of high school services with the Reston, Va.-based National Association for Secondary School Principals.
Half of all cases of mental illness begin by age 14, according to the National Institute of Mental Health. But it can take decades for those affected to get the treatment they need.
"Most of these kids aren't acting out, they're acting in," Riddile said. "And kids that act in often get overlooked."
Add to that schools grappling with growing class sizes and shrinking budgets, many are struggling to provide essential psychological and social services, according to Riddile.
"We've seen about four years of budget cuts across the country, and ironically the people who are most in need tend to get hurt the worst," he said. "But if we see a behavior that might need attention, we have to bring attention. We can't use lack of resources as an excuse."
While parents may know their kids best, schools are in a special position to compare behavior between students and spot worrying differences. Doctors say parents often lack the "professional detachment" that may lead to a useful diagnosis.
"That's difficult for parents to do," said Dr. Sandro Galea, chair of epidemiology at the Columbia University Mailman School of Public Health. "I think it's a tough to wrap your head around your kids needing treatment for anything, but we may be even more reluctant to accept the notion of mental illness."
But while schools play an essential role in recognizing the need for mental health services, their reach is limited.
"Schools cannot prescribe treatments, nor should they," said Galea, adding that only parents have the power to make treatment decisions. "This is where system-wide efforts to make sure mental health services are available come into play. It's a question of what our priorities are as a society, and I think kids and their well being are a priority."
With the right treatment, Galea said children and teens with mental health problems can live normal lives.
"Mental illness is increasingly being seen as an illness that needs treatment and benefits from treatment," he said. "But I think we need greater societal acceptance of the fact that mental illness is as much an illness as a physical illness."
Galea said that educators should not fear students with mental health disorders, as "the vast majority of violence is committed against them, not by them."
"Mental illness is a pathophysiological imbalance that requires treatment, not fear and stigma," he said.
Copyright 2012 ABC News Radio