OUR TEENAGERS....TIGHTENED AGES

New studies on peer pressure suggest that teens—who often seem to follow each other like lemmings—may do so because their brains derive more pleasure from social acceptance than adult brains, and not because teens are less capable of making rational decisions 

.And scientists say facing the influence of friends represents an important developmental step for teens on their way to becoming independent-thinking adults.

Peer pressure is often seen as a negative, and indeed it can coax kids into unhealthy behavior like smoking or speeding. But it can also lead to engagement in more useful social behaviors. If peers value doing well in school or excelling at sports, for instance, it might encourage kids to study or train harder. And both peer pressure and learning to resist it are important developmental steps to self-reliance, experts say.

Research suggests people are strikingly susceptible to influence as teenagers, but to what degree varies widely. In a growing body of work, including research published in April, scientists suggest that teens are more vulnerable to peer pressure than adults because they get greater pleasure from behaviors they experience as rewarding. They tend to find being liked by other people very gratifying.

Peer influence during adolescence is normal and tends to peak around age 15, then decline. Teens get better at setting boundaries with peers by age 18 according to Laurence Steinberg, a psychology professor at Temple University.

During puberty, people experience an increase in novelty-seeking, demonstrated by interest in exploring a new environment.

"It is adaptive to have a [biological] system that encourages you to start exploring outside the home, to start making your new own peer circles," says Beatriz Luna, a developmental cognitive neuroscientist at the University of Pittsburgh Medical Center who studies peer influence and the adolescent brain.

In years past, people thought teens didn't have fully developed frontal lobes, the part of the brain critical for decision-making and other more complex cognitive tasks. But a growing body of work seems to show that teens are able to make decisions as well as adults when they are not emotionally worked up.Instead, the key may be that the reward centers of the brain get more activated in adolescence, and seem to be activated by our peers. This heightened rush of neurotransmitters brings the teenager more pleasure than the same experience might in an adult, Dr. Luna says.

In addition, the connections between the frontal lobes and other parts of the human brain are still forming into one's 20s. That means the ability to make decisions when emotional—and peer pressure often induces emotion—isn't at full strength in the teenage years.

"It's not that they don't understand the risks involved," Dr. Luna says.

In terms of who is most resistant to peer pressure, researchers have identified some characteristics of kids who are resilient against peer influence, such as those who are more popular, have families with low dysfunction and have high communication skills. But they still don't know why these kids are less susceptible, according to Mitchell Prinstein, a psychology professor at the University of North Carolina at Chapel Hill, who studies popularity and peer influence.

Though peer pressure affects all kids, risky, "bad" behaviors like drinking tend to be associated with being popular, so kids who are less popular or have lower self-esteem tend to fall prey to peer influence for these behaviors rather than, for instance, doing well in school.

In a series of studies, including one published last year in the journal Alcoholism: Clinical and Experimental Research, researchers set up an Internet chat room and led kids to believe they were interacting with three peers who were considered popular or unpopular. The kids were then asked questions like, "Imagine you're in a party scenario and someone offers you alcohol. What would you drink?" If the other people in the room say yes, the effect is "very powerful," says Dr. Prinstein. "We find our respondents dramatically change their response."

When the supposed peers are popular, highly socially anxious kids indiscriminately conform—they would agree with whatever the other kids decided—but low-anxiety kids were more choosy. The kids most likely to be influenced are the least popular—not necessarily because of low self-esteem but because they want to be positively evaluated to fit in.

Another factor that seems to affect peer influence is ethnicity. When the chat room was filled with Caucasians, nonwhites weren't substantially affected by the Caucasians' responses, though it's not possible from the study to conclude why, Dr. Prinstein says. It could be that nonwhites are not as influenced by peers or people outside their own ethnic group.

Also, some of what appears to be resistance to peer pressure is just about wanting to be different. Some people have a higher need for uniqueness, but they're still being influenced, says Jonah Berger, a marketing professor at the University of Pennsylvania who studies social influence and consumer decision-making.

Kids from different social circles may wear very different clothing from people in other cliques, but resemble each other, even those outside the mainstream. For instance, a group of friends may sport Mohawk haircuts in reaction to other kids in school wearing preppy gear.

Warm parenting with strict boundaries, so-called "authoritative parenting," is linked to kids who are more independent thinkers. But, Temple's Dr. Steinberg warns, in order for kids to develop the ability to stand up to peer pressure, parents are going to have to let their children stand up to them, too.

"If you're the kind of parent that raises your children with the 'do it because I said so' approach, you're raising a child who's going to be more susceptible to others saying, 'Do this,' " Dr. Steinberg says.

Parents can also help their children anticipate situations of peer pressure, like declining alcohol at a party, and go over strategies to help a child save face while still avoiding an activity. "Sometimes, just having a prepared response can help a teenager get off a runaway train," says Dr. Steinberg, who is also the author of "You and Your Adolescent."

Parents should thoroughly assess their kids' friends, says Dr. Steinberg. It's better to start early and express opinions. Once a child reaches adolescence, friends may wield more influence than authority figures, so simply saying a child isn't allowed to hang out with a particular friend anymore may be met with resistance.

Instead of banning that friend outright, starting a dialogue could get better results. If they have concerns, parents should try to elicit more information, like asking their daughter why she likes a friend who concerns them.

Lorenzo Cancian-Kavoliunas, a 19-year-old Montreal college student, thinks he was able to resist peer pressure more as his confidence grew when he made good friends and began excelling in sports. "It went from below the ground to the heavens," he says.

Having good friends "turns you into a leader," Mr. Cancian-Kavoliunas says. "You don't feel like you have to fit in. You are in.