Here's an easy, nag-free way that may minimize the likelihood your elementary or middle schoolers will experiment with tobacco or booze: Ban R-rated movies and videos.

Researchers at Dartmouth Medical School who surveyed 2,600 children ages 9 to 12 and their parents found that kids whose parents did not let them watch R-rated films were 40 percent less likely to consider using cigarettes or alcohol than those with more-permissive parents. Previous studies have found that teenagers are more likely to try a cigarette if their favorite movie stars smoke — one reason anti-smoking programs have sought to reduce on-screen puffing.

The researchers found that 45 percent of children in grades 4 through 6 from 26 schools in New Hampshire and Vermont said they were forbidden to watch R-rated movies, with or without a parent. Movies rated R require an accompanying parent or adult for viewers under 17. Their content is considered more adult because they contain sex, violence or profanity.

The number of children overall who had friends who smoked or drank was low: 9 percent in each category.