THE U.S. SUPREME COURT last month ruled 5 to 4 that juveniles convicted of non-homicide crimes may not be sentenced to life without parole.

In the case, Graham v. Florida, the court followed essentially the same reasoning it used when it declared in 2005 that juveniles may not be executed: Scientific evidence is conclusive that young people have "limited moral capability" for their crimes - and their punishment should reflect that fact.

Adolescents' "capacity for change" means that, after serving substantial time in prison, they could very well be able to lead productive lives. Or maybe not. But they should be given a meaningful chance to make that case, the court ruled.

The decision will have an immediate effect on 129 prisoners around the nation - most of them in Florida - who are serving life without parole for crimes in which no one died. But the court's reasoning leads directly to the conclusion that no juvenile should receive a life-without-parole sentence, even for murder. Proposed legislation on the national and state level would require that juvenile lifers get a chance to show that they have been rehabilitated.

Across the nation, there are more than 2,500 lifers who committed their crimes as juveniles. There are 444 juvenile lifers in Pennsylvania, all convicted of homicide - the most in the nation.

Last September, state Rep. Kenyatta Johnson, D-Phila., introduced legislation (H.B. 1999) that would require that prisoners serving life sentences for crimes committed when they were juveniles be given at least one parole hearing during their first 15 years in jail, and at least one every three years after that. Johnson's bill is similar to one being considered in the U.S. House of Representatives. We support it.

Even though he didn't mean to, Justice Clarence Thomas, in his dissenting opinion, provided an argument that supports this view - but not before presenting an "originalist" view of the Constitution that is nothing short of breathtaking. Thomas pointed out that, when the Bill of Rights was adopted, children as young as 7 could be executed - as if nothing has changed since then.

It's impossible to believe that the Founders, if they had access to the current scientific evidence on a range of subjects, would fail to take it into account when writing the nation's laws. And that evidence says: The parts of brain that govern foresight, self-control, susceptibility to peer pressure and the ability to consider in advance the consequences of one's actions are not as fully developed among adolescents. Which also means that they have a capacity to change that is greater than that of adults.

Thomas did observe that, given the court's rationale, there is no substantial difference between the culpability of a juvenile who rapes a child but doesn't kill her and another adolescent who pulls the trigger and kills someone. Both are unspeakable crimes, but if a juvenile is deemed "mentally immature" for one, he is "mentally immature" for the other.

Justice Anthony Kennedy referred to the Court's 2005 decision in the most recent one: "From a moral standpoint, it would be misguided to equate the failings of a minor with those of an adult," he wrote. That should go for all juvenile crimes.

No one is suggesting that an adolescent who takes a life should not be punished - only that it is "cruel and unusual punishment" to deprive him of any chance for release.

Prison doors should bang shut on juvenile killers - and stay shut for a good long time. But society shouldn't throw away the key.