The number of teenagers being held in detention centers and other facilities across the country is at its lowest level in 35 years, a finding that suggests a national shift on how to treat young offenders, juvenile justice advocates say.

Even better, those experts say, is that as fewer teenagers are locked up, a steep decline in juvenile crime has followed.

"For so long, our response to issues of crime and public safety has been 'We need to lock up more people,' " said Bart Lubow, director of the juvenile justice strategy group for the Baltimore-based Annie E. Casey Foundation, which published a report on the findings last week.

"But people are seeing that the trends don't necessarily follow that, certainly not when it comes to young people, who are often better served by different treatment methods."

Though the report, "Reducing Youth Incarceration in the U.S.," found that Pennsylvania was one of six states that posted a slight increase from 1997 to 2010 in the number of juveniles who were confined, advocates said those numbers did not represent the progress the state has made in dealing with teenagers who run afoul of the law.

James Anderson, executive director of the state Juvenile Court Judges' Commission, which oversees juvenile justice practices and advises the state's juvenile courts, said that from 2008 through 2011, Pennsylvania's court-ordered placements of juveniles into detention centers and other delinquency programs has decreased by more than 25 percent.

The data measured in the Casey Foundation report also includes the placement of juveniles into some residential programs and short-term programs that are seen as more therapeutic than punitive, Anderson said, such as residential facilities that help teenagers develop coping strategies.

Additionally, at least three of the state's juvenile detention facilities closed in recent years due to underuse, Anderson said.

"Good things are being done and good decisions are being made as far as how to deal with young people," he said.

Teenagers are still developing their decision-making capabilities in crucial ways, according to a number of recent studies, Anderson and Lubow said. Teenagers who struggle with social skills and act out are often struggling with family problems, abuse or mental health issues.

Those teenagers are particularly vulnerable to the harsh realities of living in a detention center, and many could benefit more from intense counseling, outpatient programs or a more therapeutic setting.

"If we put them in institutions where they are traumatized emotionally and physically, we're pursuing a public policy that is the equivalent of shooting ourselves in the foot," Lubow said.

Contact Allison Steele at 215-854-2641 or asteele@phillynews.com