Pop quiz for parents: When it comes to smoking, the opinions that count the most with your kids are those of: A.) His or her peers. B.) You, the parents.

The answer is B. If you tell them smoking is very, very bad, they're less likely to do it, according to a new study by Dartmouth Medical School researchers.

The results of this study, reported in Pediatrics (Vol. 108, No. 6: 1256-1262), add to a growing body of evidence that parents have more influence on their teens than they may have realized.

"Tell your kids that you expect them never to smoke and that they will be punished if they do," advises lead author James D. Sargent, MD, associate professor of pediatrics and adolescent medicine at Dartmouth. "Remind them of this from time to time. Steer them away from peers who smoke."

Parents should be aware that smoking is just as serious as marijuana, alcohol, and other drugs, said Ron Todd, director of tobacco control for the American Cancer Society.

"Sometimes parents are less concerned about tobacco than other illicit drugs," Todd said. "In fact, far more young people are going to become addicted to tobacco and die as a result of it, than of all other illicit drugs combined."

And tobacco is an illicit drug for anyone under 18, Todd said.

Sargent and co-author Madeline Dalton, PhD, studied hundreds of rural Vermont children and teens attending three K-12 schools. They questioned the students over a three-year period, and also noted whether the students were smokers.

Each year, the youths were asked this question: "How do you think your mother/father would react if you were smoking cigarettes and she/he knew about it?"

A response of "She/He would tell me to stop and be very upset," was an example of an answer that indicated strong parental disapproval.

The youths who indicated their parents would disapprove were less than half as likely to become established smokers, compared to those who did not think their parents would strongly disapprove, according to the study.

Over the three-year period, students who saw their parents as becoming more lenient were significantly more likely to become established smokers, the authors wrote.

As for peer pressure to smoke — it doesn't count as much as parental disapproval, the study found. Those students whose peers smoked were less likely to go along with the crowd if both parents strongly disapproved of smoking, the authors wrote.

What if the parents smoke? Even when the parent was a smoker, teens were less likely to smoke if their parents disapproved of them smoking. It's a classic "do as I say, not as I do" situation, but the teens in this study accepted it.

Sargent, an epidemiologist, said he was not surprised to find that parental approval was a stronger influence than a parent smoking.

"In many ways, parent smoking can turn a kid off to smoking because they then see what smoking is like in reality — as opposed to the way it is depicted in movies and advertising," Sargent said. "In addition, kids can separate what parents do from what they expect the kid to do."

Sargent said some parents who smoke might feel guilty about turning around and telling their children not to.

"This should not keep them from talking about what it is like to be addicted to tobacco, how hard it is to quit, how they started — they probably started as teens never thinking they would get hooked — and how much they want to quit," Sargent said.

"Smoking parents can also be effective at setting non-smoking rules for their kids," he said.

Past studies have shown that kids are less likely to smoke if they believe they will be punished for it, and that kids from households that prohibit smoking are less likely to smoke, Sargent said.

"You show your kid you love him or her by setting rules and limits and enforcing them," he said. "Kids get upset when punished, but if you talk to them and listen to their concerns — and continue to be firm — they ultimately feel closer to you, the parent."

Didn't the parents of a few generations ago know this?

"Parents in the 50s tended to set rules but were not very good at listening to their kids," Sargent said. "Research has shown that the best parents are those who can balance the rule- and limit-setting with communicating and being responsive to their kids' feelings and concerns.

"Baby boomers are more responsive but are less good at setting rules," Sargent said. "They are indulgent parents."