After his father was diagnosed with cancer, a 15-year-old Champaign, Ill., boy started skipping school, erupting in angry outbursts, yelling at teachers and punching holes in walls or retreating to his room paralyzed by an overwhelming sadness.

When the teen's assistant principal approached him a few months ago about seeking help for mental illness, the student initially declined, saying he didn't need it. However, eventually he did seek treatment. Diagnosed with major depressive disorder, he joined group therapy sessions at his school.

No consistency in screening

As stories about increasing school violence dominate headlines, experts say many teens are struggling with untreated mental illness. However, even though federal health officials recommended universal mental health screenings for students nearly a decade ago, they still aren't required.

An Associated Press review of policies around the nation shows screenings vary widely not only from state to state, but within each school district. There's no consistency on whether the schools screen, what age they screen and what they screen for.

"We have [schools] screening for all kinds of rare infectious diseases and then we don't screen for common behavioral disorders that are costly to the individual, the family and society in terms of health care utilization, crime cost and high risk of death … it doesn't make any sense from a public health perspective," said Mike Dennis, of Chestnut Health Systems in Normal, Ill. He teaches clinicians in 49 states how to assess and treat patients with mental ­illness and substance abuse.

Although the 15-year-old Illinois student was not diagnosed through a school program, in his school-based group therapy he's learning practical tips to identify his triggers and calm them before emotions spin out of control.

"I think it is a good idea because a lot of people think they don't need help but they actually do," said the teen, who is not being identified because he is a minor.

The federal government does not keep track of school mental health screening, so it's all but impossible to say how many schools do or don't offer it.

The offerings vary from intensive services to virtually none at all.

"No state is providing high-end services in all of their schools," said Sharon Stephan, co-director of the Center for School Mental Health, a national organization based at the University of Maryland that provides training for schools and ­mental health providers.

Surveys in Minnesota

Baltimore and Chicago have robust screening and treatment programs. Teachers in one south Florida school district screen ­children as young as kindergarten by filling out a short questionnaire, while students in Minnesota answer anonymous surveys about drug use and depression. In Olympia, Wash., 21,000 students were screened for substance abuse and mental health issues in 2010, but that dropped to only 7,500 in 2012 due to lack of funding.

Mental health problems typically start during adolescence. If left untreated, they can lead to substance abuse, school drop outs and difficulty maintaining steady jobs and relationships. Yet many people are not diagnosed until later in life when they don't have access to services because they don't have health insurance or their insurance doesn't cover it.

The U.S. surgeon general reports that 10 percent of children and adolescents suffer from serious emotional and mental disorders that significantly affect their daily lives.

However, offering mental health screening in schools can raise other complex issues. Some warn that mass screenings will overdiagnose students and stigmatize them with a lifelong label.

"People have to be very cautious when they are talking cavalierly about screening these kids. How do people feel if they are over-identify or under-identify? … The consequences to that are big," said Linda Juszczak, president of the School-Based Health Alliance, a group that advocates for school clinics.