While voters who approved California's Proposition 21 may not agree, some courts have begun to affirm what scientists have asserted for some time: that adolescent brains function in ways significantly different from adults.

In a federal case ordering the release of convicted second-degree murderer Robert Rosenkrantz, the court held that "The susceptibility of juveniles to immature and irresponsible behavior means their irresponsible conduct is not as morally reprehensible as that of an adult."

And in a ruling in September ordering an overhaul of the state's parole board, Santa Clara County Judge Linda Condron wrote that age is an especially important factor when the impetus behind a shooting is "youth group or gang rivalries, posturing, and threats which mature adults would not have been caught up in."

When the U.S. Supreme Court overturned the death penalty for juveniles in 2005, it did not cite scientific research, but it did hold that a minor's "culpability or blameworthiness is diminished, to a substantial degree, by reason of youth and immaturity."

Advocates such as the Juvenile Justice Center of the American Bar Association and Human Rights Watch have used science to argue against the death penalty and life without parole for minors.

Recent brain research suggests that the areas governing judgment, emotions and decision-making are often not fully developed until the early 20s.

Daniel Weinberger, director of the Clinical Brain Disorders Laboratory at the National Institutes of Health, said the difference between teens and adults lies in the frontal lobe and its prefrontal cortex that allows adults to act "on the basis of reason."

That area functions poorly in adolescents, scientists say, while another area that controls aggression and impulse is more dominant. That makes teenagers "more prone to react with gut instinct," said Harvard Medical School researcher Deborah Yurgelun-Todd.

"I think the frontal lobe, that part of the executive region that we studied, is not always functioning fully in teenagers; or least our data suggests that perhaps it's not," Yurgelun-Todd said in an interview with PBS "Frontline."

"That would suggest that therefore teenagers aren't thinking through what the consequences of their behaviors are, which would lead us to believe that they'd be more impulsive, because they're not going to be so worried about whether or not what they're doing has a negative consequence."

In his standard textbook on adolescent psychiatry, Yale researcher Melvin Lewis writes that emotionally speaking, the teenager is "really both part child and part adult."

But former Monterey County prosecutor David Alkire, who tried five minors in adult court for a 2002 gang shooting case, said such arguments are irrelevant.

"The overwhelming majority of teens don't join gangs and pick up guns and go out and shoot people," he said. "The fact that a tiny minority do it is no reason to give them some benefit of the doubt that if they had better judgment and were acting as adults, they wouldn't have done this."

A father of a teenager, Alkire said no one would argue that teenagers have fully developed impulse control.

"Nobody in the world thinks juveniles exercise excellent judgment. ... but when you talk about violent gangs who act out, it becomes far more important to protect the community."

|— Julia Reynolds