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A federally funded study that involved scanning more than 12,000 connections in the brains of 238 volunteers ages 7 to 30 found that the technique appeared to accurately differentiate between the brains of adults and children and determine roughly where individuals scored in the normal trajectory of brain development.

While much more work is needed to validate and refine the test, the technique could have a host of uses, including providing another way to make sure children's brains are developing properly, in the same way doctors routinely measure other developmental milestones. The scan could, for example, identify children who might be at risk for autism, schizophrenia and other problems because their brains are not maturing normally.

"If you are worried about a kid's development, in five minutes you could do a scan and it would spit out a measurement of their brain maturity level," said Nico Dosenbach, a pediatric neurology resident at St. Louis Children's Hospital who helped develop the technique described in Friday's issue of the journal Science. "That's sort of the future."

But the test might be open to premature use or abuse, experts warn. Will overly anxious or competitive parents demand that their children be tested to see how they score compared with their peers? Or to help them decide whether children are mature enough, for example, to leave home for college? Will online dating services offer brain scans rating the maturity of potential mates? Will defense lawyers try to use scans to prove their young clients aren't mature enough to be tried as adults? Or will prosecutors cite the scans to prove the opposite?

Lawyers have already attempted to use other types of brain scans as high-tech lie-detector tests, even though scientists say the scans are far from ready.

"I could imagine someone taking a minor who would have been charged under one set of law and say, 'No, look. They have a brain that has greater maturity and we should try them as adults,' " said Joseph Fins, chief of the division of medical ethics at Weill Cornell Medical College in New York. "I'm concerned about the potential misuse of the nascent technology."

Fins and other experts noted that the public has a tendency to oversimplify and exaggerate the power of brain scans.

"Ultimately, the question for all these kinds of studies is: Does the brain imaging tell us more than we would learn by observing or asking or examining the participants?" said Anjan Chatterjee, a neuroscientist at the University of Pennsylvania. "Maybe this represents a step towards that possibility, but we are not there yet."

Factors such as upbringing and other environmental influences remain important, several experts noted.

"There is a strange hold that neuroscience has on people, as if it is more real than what we know from observation," Chatterjee said in an e-mail. "So, yes parents might want such scans, but it is not clear that it would tell them something about their child's maturity that they don't already know - or a careful observer already knows. As for boyfriends, maybe Internet dating sites could post such scans (maturity years). But the same applies. The woman in question could probably ask trusted friends and get a straight answer."

The technique developed by Dosenbach and his colleagues uses magnetic resonance imaging, already commonly used to measure activity in the brain by correlating increases and decreases in blood flow to various brain regions. The scans are considered safe because they do not use radiation.

In this case, the technique was called functional connectivity magnetic resonance imaging, or fcMRI, because it measured connections in the resting brains of the subjects. The researchers used a computer program to analyze how connections in the brain changed as the mind matured, pinpointing 200 to produce an index of maturity. They found that close connection weakened while distant connections strengthened as the brain matures, until about age 21 or 22.

"This paper represents a major step forward," said Jay N. Giedd, chief of the brain imaging unit at the child psychiatry branch of the National Institute of Mental Health. The research "represents the next major paradigm shift, looking at 'connectivity,' or the relationship amongst subcomponents of the brain," he said. "High impact for sure."

Dosenbach estimated they were able to distinguish between the brain of children ages 7 to 11 and that of adults ages 25 to 30 with 90 percent accuracy. They were able to differentiate between adolescents and adults with 75 percent accuracy, Dosenbach said in an e-mail.

But Dosenbach warned that it would be premature to start using the technique to measure individual maturity levels.

"I would not endorse that," he said.