The emotional maturity of adolescents lags behind their intellectual maturity, a fact that may explain why teenagers are more susceptible to temptations, a recent study showed.

Teenagers' intellectual capacity may be on a par with that of adults, but they don't have the same control over their emotions, said a study published on Monday in the October issue of American Psychologist, a journal of the American Psychological Association.

Teenagers may understand, for example, that stealing beer is wrong, but they may be too susceptible to peer pressure and their emotions to make a responsible decision, lead researcher Elizabeth Cauffman, a professor of psychology and social behavior at the University of California in Irvine, said in a news release.

The researchers studied people with an age range of 10 to 30 years. They interviewed them and had them fill out questionnaires that measured their psychosocial maturity and basic intellectual acumen.

The study could be used in two cases before the US Supreme Court next month that would consider the constitutionality of sentencing juveniles to no-parole life prison sentences, said Cauffman.

Also involved in the study were researchers from Georgetown University, the University of California in Los Angeles, the University of Colorado at Boulder and Temple University.

"Any parent of an adolescent can tell you they often ask them: 'Why did you do that?' and the typical response is, 'I don't know,' " Cauffman said. "Adolescents aren't stupid. They're very smart people, but they do a lot of stupid things, so we decided to consider if they're smart, then why do they do stupid things?"

The impetus for the study was an apparent contradiction in legal positions the American Psychological Association took in 1990 and 2005 cases, Cauffman said.

In 1990, the association argued in an abortion case that adolescents and adults had the same cognitive abilities. But in 2005, the association prepared another legal brief on the death penalty that said adolescents and adults had different cognitive abilities, Cauffman added.

Supreme Court Justice Antonin Scalia pointed out the apparent contradiction, so Cauffman and the other researchers got to work, Cauffman explained.

Adolescents were better able to make a decision about an abortion because they had time to consider their options and often made those decisions with adults, Cauffman observed. But crimes committed by juveniles were often done in groups, the result of peer pressure or spur-of-the-moment impulses, she added.

"We can all think back to adolescence and remember a moment when we think: 'Why did I do that?' " Cauffman said. "We call it starting the engines without a skilled driver. Sure, the car runs, but the person behind the wheel doesn't know how to operate it well yet."

The researchers were not arguing that because of emotional differences between adolescents and adults, teenagers should not be held accountable for their crimes, Cauffman cautioned.

"It's how they should be held accountable is what's very important," Cauffman said, adding authorities needed to consider how emotionally underdeveloped adolescents were.

The researchers found that people might not be able to resist peer pressure or fully control their impulses until after they reach age 22.

The two cases up for review by the US Supreme Court involve Joe Sullivan, who was sentenced to life in prison without the possibility of parole in 1989, and Terrance Graham, who was sentenced to the same term in 2005.

Sullivan was 13 years old when he and two older boys robbed and raped an elderly woman after breaking into her home.

Graham was 16 when he robbed a restaurant with two accomplices. A year later when he violated probation, a Florida judge sentenced him to life in prison.