They teach kids to read, write and solve math problems, and to work and play well with others.
And along with those lessons, educators are increasingly being trained to spot depression, anxiety and other troubling behaviors in their students, with administrators and teachers forming the first line of defense against mental illness.
"We provide psychiatric first aid," said Ailleth Tom, who coordinates crisis counseling and mental health services for the Los Angeles Unified School District. "We really listen, protect and connect students with services.
"We don't ask, `What's wrong with you?"' she said. "We ask, `What's happened to you?"'
Speculation about the mental health of the 20-year-old gunman in the Connecticut school shootings has focused attention on the need for the early treatment of troubling behavior in the nation's adolescents and teens.
Los Angeles Unified has long partnered with local law enforcement agencies and mental health experts in Los Angeles County, where crisis- and threat-assessment teams evaluate student activity that could potentially lead to violence.
Within Los Angeles Unified, experts train principals and faculty to watch for early warning signs so kids can get help before more serious conditions develop. Any new insights that develop from the Sandy Hook Elementary tragedy will be incorporated into future professional development sessions, officials say.
"We all are very aware of the school's role in identifying problems a student may be having. We do feel that responsibility," said Judith Perez, president of Associated Administrators of Los Angeles, which represents about 3,000 principals and assistants principals in LAUSD.
With 600,000 students, LAUSD has a cadre of 300 psychiatric social workers who refer students to mental health professionals or, in some cases, hold group or individual therapy sessions on campus for kids struggling with emotional traumas like divorce, death, illness or abuse.
"They're completely busy all of the time," Superintendent John Deasy said. "There are not enough of them to deal with the problems."
Mental health services are also offered at eight clinics operated jointly by LAUSD and Los Angeles County. Sites include clinics next to Daniel Pearl High School in Lake Balboa, and at Cabrillo Elementary in San Pedro.
Christine MacInnis, a counselor at North High in the Torrance Unified School District, said counselors do not wait for students in distress to come to them.
"Half come to me on their own, and the other half are referred through a parent, teacher, coach or administrator," she said. "Teachers are probably our first line of defense, because they are the ones with them all day."
The most common warning signs are sudden changes in behavior or appearance. A strong student may lose interest in his studies, for instance, or a snappy dresser may start coming to school looking disheveled.
If Torrance High counselors suspect that a student is a danger to himself or others, they call in a Los Angeles County psychiatric evaluation team. In the extremely rare event that a child is perceived to be a threat to others, law enforcement is also notified.
In 2011-12, the Los Angeles County Department of Mental Health conducted more than 4,200 threat assessments involving the region's school districts, a spokeswoman said. The agency's Emergency Outreach Bureau also held some five dozen training sessions for educators, law-enforcement, parents and students.
The Sandy Hook tragedy unfolded as many school districts were preparing for winter break. Nevertheless, officials began reviewing their own operations to determine whether they needed to do more to keep campuses safe.
San Bernardino City Unified, for instance, formed a task force that includes officers from the San Bernardino and Cal State San Bernardino police forces, along with members of local churches and service clubs. They'll be looking at all aspects of student safety, including support for youngsters with mental health issues.
According to the National Alliance on Mental Illness, more than 20 percent of U.S. kids ages 9-17 are struggling with a mental disorder that disrupts their lives, with symptoms appearing by age 14 in half of those cases.
However, only 20 percent of these youngsters begin treatment each year.
Experts say parents may be reluctant to seek treatment for their child because of the long-held stigma about mental disorders. Others may be in denial about troubling changes in their child's behavior, dismissing extreme mood swings, or episodes of panic, defiance or excessive hostility as just a passing phase.
This may create a delay that experts say could allow the disorder to worsen and become more difficult to treat.
"Adolescents and teens are in the midst of achieving their education, making friends and developing their identity," said Dr. Daniel Grosz, director of adolescent psychiatry at Northridge Hospital Medical Center's Behavioral Health Unit.
"If their mental illness started early in life, it's harder for them to achieve these goals. The longer we delay, the more resistant these conditions become."
Researchers from the National Institute of Mental Health studied more than 10,000 kids with mental disorders and found that panic and anxiety were the most prevalent issues, followed by ADHD, depression and drug or alcohol abuse.
Grosz said youngsters coping with these kinds of issues may display flashes of anger or aggressive behavior, but not the type of violence unleashed at Sandy Hook Elementary, where 20 children and six adults were gunned down.
"It's important after a tragedy like this to strike the right balance between investing in awareness and resources and referrals without going to the other extreme of suspecting any kind of unusual behavior," he said.
Nevertheless, he advised against keeping guns in a home where there are concerns about the mental health of anyone - adult or child.
While the Sandy Hook shootings shook the entire nation, they had an even stronger impact on the parents of children with mental and behavioral disorders.
Rosa Morales, who lives in San Bernardino County, has sought psychological help through the school system for her 10-year-old son because of the sudden, angry outbursts that seem to come out of nowhere.
"Once he had a screaming fit when he couldn't pass a level in a reading computer game," she said. "He yelled and screamed that he was a dummy, that all the kids in his class had already passed the level and that he was too dumb to get it right," she said.
Morales fears that her son's tantrums may one day escalate to violence.
Administrators said schools can play an important role beyond recognizing students in distress. They can help parents find low-cost counseling, support groups and other services.
In the wake of the Sandy Hook Elementary tragedy, school districts in the Southland and around the U.S. have been reviewing security procedures and looking for ways to improve student safety.
However, Las Virgenes Superintendent Dan Stepenosky, who wrote his doctoral dissertation on the gunmen in two high-profile school shootings, said the best way to protect students is to get to know them well and to address their mental health issues as soon as they surface.
Staff Writers Rob Kuznia and Beatriz E. Valenzuela contributed to this report.
Warning signs of mental illness
Each mental illness has its own symptoms, although there are some general signs that might alert you that someone needs professional help. These include:
Marked personality change
Inability to cope with problems and daily activities
Prolonged depression and apathy
Marked changes in eating or sleeping patterns
Thinking or talking about suicide or harming oneself
Extreme mood swings - high or low
Strange or grandiose ideas
Abuse of alcohol or drugs
Excessive anger, hostility, or violent behavior.
Source: National Institute of Mental Health