Scientists: Teen Brain Still Maturing

Sheila Montgomery and her son Zack, 17, are shown, Tuesday, Nov. 20, 2007, at their home in Portland, Ore. (AP Photo/Rick Bowmer) (Rick Bowmer - AP)

Steinberg said he thinks courts should be able to punish some 16- or 17- year olds as adults. That would be reserved for repeat violent offenders who've resisted rehabilitation by the juvenile justice system, and who could endanger other youth in the juvenile system if they returned. "I don't think there are a lot of these kids," Steinberg said.

For the rest, he thinks it makes sense to try rehabilitating young offenders in the juvenile justice system. That's better than sending them through the adult system, which can disrupt their development so severely that "they're never going be able to be a productive member of society," Steinberg said. "You're not doing society any favor at all."

Ash said that to decide whom to treat as an adult, courts need some kind of guideline that combines the defendant's age with the crime he's accused of. That should leave room for individual assessments, he said.

But "we don't have very good measuring sticks" for important traits like how impulsive a juvenile is, he said.

In any case, the decision for each defendant should balance a number of reasons for punishment, like retribution, protecting society, deterring future crime, and rehabilitation, said Ash, who's a member of the American Psychiatric Association's Committee on Judicial Action.

Even if a 14-year-old murderer is held morally responsible for the crime, he will have matured by the time he's 18, and in the meantime he may be more amenable to rehabilitation than an adult murderer is, Ash said.

In fact, most experts conclude that rehabilitation works better for juveniles than for adult offenders, he said.

And just as parents know how irrational juveniles can be, Ash said, they also know that rehabilitation is a key goal in punishing them.

"What we really want," he said, "is to turn delinquent kids into good adults."

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On the Net:

American Psychiatric Association statement on youth sentencing: http://www.psych.org/edu/other_res/lib_archives/archives/200507.pdf

Psychiatrists' brief in Supreme Court case: http://www.abanet.org/crimjust/juvjus/simmons/ama.pdf

American Psychological Association brief: http://www.apa.org/psyclaw/roper-v-simmons.html

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AP National Writer Sharon Cohen contributed to this story.