THE SUPREME COURT declined this week to reconsider a 13-year-old decision permitting executions of convicts who committed their crimes while they were still juveniles. Four justices dissented, arguing that the logic of the court's ban last term on executing retarded people applied also to the juvenile death penalty -- that a consensus had developed that the practice was cruel and unusual punishment that violated the Constitution's Eighth Amendment. Unsurprisingly, a majority of the court disagreed, leaving the states free to continue killing kids.

The juvenile death penalty -- with its arrogant assumption that society can judge whether someone who is still a child will prove redeemable over the course of his life -- is one of the least defensible aspects of American capital punishment. It is impossible to contend seriously that many youthful killers will be deterred by the threat of execution years later. And while the dissenters can be accused of seeking to impose their policy preferences in this area on the states, the court's prior cases have not exactly provided a model of reason. According to current case law, it's fine for a state to execute someone for crimes committed at 17 or even 16. But 15 is beyond the pale. Exactly where, one is entitled to ask, does the Constitution make that principled distinction?

Justice Antonin Scalia, in a recent article, derided the court for drawing such lines, noting correctly that age limits are its own creation. The Eighth Amendment, he argued, prohibits now only what it prohibited in the 18th century -- and the execution of children was okay then. But nearly a century ago, the court rejected so stark an approach to the amendment, and the one it ultimately adopted instead -- which reads the Constitution as forbidding whatever punishments society evolves to regard as cruel and unusual -- requires the court to draw this line somewhere. Distinguishing between legal childhood and adulthood seems a far more rational place to put it than between the sophomore and junior years of high school.