WASHINGTON (AP) -- The Supreme Court ruled Tuesday that the Constitution forbids the execution of killers who were under 18 when they committed their crimes, ending a practice used in 19 states.

The 5-4 decision throws out the death sentences of about 70 juvenile murderers and bars states from seeking to execute minors for future crimes.

The executions, the court said, violate the Eighth Amendment ban on cruel and unusual punishment.

The ruling continues the court's practice of narrowing the scope of the death penalty, which justices reinstated in 1976. The court in 1988 outlawed executions for those 15 and younger when they committed their crimes. Three years ago justices banned executions of the mentally retarded.

Tuesday's ruling prevents states from making 16- and 17-year-olds eligible for execution.

"The age of 18 is the point where society draws the line for many purposes between childhood and adulthood. It is, we conclude, the age at which the line for death eligibility ought to rest," Justice Anthony Kennedy wrote.

Juvenile offenders have been put to death in recent years in only a few other countries, including Iran, Pakistan, China and Saudi Arabia. Kennedy cited international opposition to the practice. (Notice the exclusive club of nations we've been admitted to who still legalize killing little children for sport. --ed.)

"It is proper that we acknowledge the overwhelming weight of international opinion against the juvenile death penalty, resting in large part on the understanding that the instability and emotional imbalance of young people may often be a factor in the crime," he wrote. (Kennedy, show me where the heck it says we should confer with international law in the AMERICAN CONSTITUTION!??!?! --ed.)

In a dissent, Justice Antonin Scalia disputed that there is a clear trend of declining juvenile executions to justify a growing consensus against the practice.

"The court says in so many words that what our people's laws say about the issue does not, in the last analysis, matter: 'In the end our own judgment will be brought to bear on the question of the acceptability of the death penalty,"' he wrote.

"The court thus proclaims itself sole arbiter of our nation's moral standards," Scalia wrote. (Boo-yea! Did I just see this in print??? --ed.)

Justices were called on to draw an age line in death cases after Missouri's highest court overturned the death sentence given to Christopher Simmons, who was 17 when he kidnapped a neighbor, hog-tied her and threw her off a bridge in 1993. Prosecutors say he planned the burglary and killing of Shirley Crook and bragged that he could get away with it because of his age.

The four most liberal justices had already gone on record in 2002, calling it "shameful" to execute juvenile killers. Those four, joined by Kennedy, formed Tuesday's decision: Justices John Paul Stevens, David H. Souter, Ruth Bader Ginsburg and Stephen Breyer.

Chief Justice William H. Rehnquist, Justice Clarence Thomas and Scalia, as expected, voted to uphold the executions. They were joined by Justice Sandra Day O'Connor.