"You let your kids see that?" "All my friends will think I'm a baby." "Everyone else sees R movies all the time."

If any of those lines has ever been uttered in your house, you may be grateful to the Montgomery County school system, which is enforcing a new policy on movies in the classroom, banning R-rated flicks from high schools and PG-13 movies from middle schools.

"You don't need to see Leonardo DiCaprio's 'Romeo and Juliet' after reading the play in ninth grade," says Montgomery schools spokesman Brian Edwards. The PG-13-rated update somehow managed to add hallucinogens and 9mm handguns to Shakespeare's classic. "It's just not necessary," Edwards says.

The handling of Hollywood's gratuitous excesses is as good a barometer as exists of differences in parenting. When my daughter was in second grade, she called us from a friend's house to beg that we come get her instantly: "They're putting on an R movie, and the mom thinks it's okay," she said in a panic. That threshold was not crossed again.

In all too many schools, teachers eager to look cool or do less work shock parents by showing movies that are not only inappropriate but of zero educational value. Some teachers have come to believe that Hollywood's version of history qualifies as fact, no matter how distorted or anomalous the show might be. So studies of ancient Rome are accompanied by scenes from "Gladiator," and the Civil War is illustrated by "Glory" and learning about the Holocaust becomes an occasion to watch "Schindler's List," whose essential message of hope negates the historical truth. (In the real story, as the great documentary director Claude Lanzmann notes, death wins.)

"We don't teach by video in Montgomery County, and I don't think any school should," says Jody Leleck, associate superintendent for curriculum.

Edwards notes that some teachers and principals are upset by the new rules. They argue that movies are a way to connect with an image-addicted generation. But as Edwards says, "If you can't go down to the corner and see it, why should we show it to them in the classroom? Why would you need to see the blood and guts of 'Saving Private Ryan' to understand the horror of D-Day?"

The problem with Montgomery's new approach is that it cedes the task of determining what's appropriate to the same Hollywood moguls who make the trash in the first place. By using Motion Picture Association of America ratings as the arbiter of what kids see, the schools buy into a system that is "getting more and more nebulous," as Jim Judy puts it. From his home in Germantown, Judy runs screenit.com, an online archive of highly detailed film analyses that let parents determine what's right for their kids.

From Judy, you learn that "Jarhead," rated R, features 278 incidences of the f-word or that "Rent" won a PG-13 despite two f-bombs. "It's all very political, and it's been sliding," he says. "Today's PG-13 films used to be rated R. You really can't tell by what the MPAA says. 'Whale Rider' was PG-13 because of two seconds of a guy holding a drug pipe. The new Harry Potter was PG-13 because people died."

Judy supports the idea of schools setting stricter limits, but he advises that teachers and principals "need to watch the movies themselves and make their own decisions, or use an independent service like mine."

Fairfax County's regulations are also based on MPAA ratings, but unlike Montgomery's, they give teachers the ability to make more nuanced judgments than Hollywood does, and they give families a say: Middle schools may use PG-13 movies with advance notice to parents, and high schools may use excerpts from R movies with written parental permission.

It makes sense to allow more flexibility at the high school level, but schools should be even stricter about age-appropriateness in the lower grades. How about no Hollywood at all for the little ones? Kids deserve a cloister from the noise of pop culture.

As with sex and drug education, in high school, the more open the discussion, the more likely it is to hit home. But in lower grades, parents should be allowed to set the pace of their kids' exposure to a harsh world.

Schools can and should be families' allies against a rancid pop culture and parents who don't know how to say no.

E-mail: marcfisher@washpost.com