The two young women sitting inches from each other in a Silver Spring living room grew up half a world apart. The French girl, an exchange student studying at Richard Montgomery High School in Rockville, and her Costa Rican guest, a former exchange student who'd recently returned to the United States, had just met.

You'd never know it. Because when it comes to what's weird about life in the United States, their observations are best-buddy similar:

On how easy American teachers are on student slackers. On how advertising is everywhere: in the schools, on billboards, even in Metro cars.

On how nobody here walks!

"You have to use the cars to go anywhere!" marvels Helene Kone, 16, of Lorraine in northeastern France. "And in the U.S., everything is a hundred times bigger."

"Like buildings," Martha Torres Solano agrees.

"And supermarkets!" Helene continues. Schoolwise, they concur, the smorgasbord of dance, art and fitness classes that U.S. high schoolers choose from is great. "In France, it's pure academics until 6 p.m.," observes Helene, who for eight months has lived in this pleasant home with her host dad, retired history teacher Stan Boyd, and his daughter, Crystal, 16.

So what's the best thing they learned as exchange students with AFS, the nation's oldest exchange student program?

"That I could live a year without family and friends," Helene replies.

"That I'm strong. But I also learned my defaults -- ," she pauses, correcting herself. "Not defaults."

"My flaws."

Oh, those. Martha, 22, learned about hers, too, during her U.S. sojourn -- which she discussed, painfully, in this column.

It's been four years since Martha, whose unrestrainable femininity briefly shattered my home's testosterone-steeped vibe, returned to San Jose. She graduated from high school, then college, then recently became a writer for a public schoolteachers' organization.

But she never forgot that AFS year: her connection to me, a daughterless girlie-woman who savored shopping, cooking and crying over chick flicks with someone who actually enjoyed them. Her headache-inducing struggle with taking high school classes in an unfamiliar language. Her unexpected battles with "brothers" reluctant to share their parents, TVs, vacations and lives with a giggly, ballet-dancing, Spanish soap opera-obsessed female.

When Martha recently returned for her first U.S. visit since leaving, I'd gotten her together with Helene, whose AFS tenure ends in three weeks. Like Helene, Martha is philosophical.

"AFS has this saying: It's not good, it's not bad. It's different," she begins. She remembers asking two male exchange students from Turkey why Muslim women "hide under all this clothing. They tell me it's tradition, but that they also want women to protect their beauty, for it to be their own."

Although she had dismissed the practice as machismo, "hearing it from their mouths, the feeling they put into it, made me understand. It wasn't good or bad. Different."

Speaking of different, did I mention the shoplifting?

In some ways, Martha's worst U.S. experience was her best. She was browsing at the Bloomingdale's in White Flint when she saw a classmate from her Silver Spring high school -- an all-American cheerleader type who snorted when Martha admitted to never having shoplifted. The cool American kids all steal, the classmate taunted. "They never get caught."

The moment that a store security guard stopped Martha with several blouses stuffed in her purse, Miss All-America evaporated. A bucket-worth of tears, one weepy court appearance and 24 hours of community service later, Martha emerged a wiser 18-year-old.

The experience "make me grow up," Martha says, in her still charmingly imperfect English. "I learn not to trust everyone from first sight. To think, 'What will happen if I do this?' "

Moved by her new insight and self-possession, I listen as she describes having briefly been infamous at AFS: Few exchange students make such spectacular errors. Still puzzled about how she did anything as uncharacteristic as stealing, she remembers the incident "like, every other day."

"Now I can laugh. . . . Say, 'I was so stupid.' "

Stupid? Try young -- and human. Arriving home from Helene's, I ask the new grown-up Martha what struck her most about her time with AFS. "Now, when I read the newspaper, if there's sad news, I remember the friends I met. I have friends everywhere," she says.

"How you going to start a war in a country where you have a friend?"

I love it. But later, she offers another answer:

"I don't have words, either in English or in Spanish, to tell how [it feels], to be part of an American family . . . where I made this big mistake, but they had enough love to forgive me."

That family never realized her terror of being rejected. "One AFS kid's family kicked him out because he didn't shower every day," she explains.

But by the time of her transgression, Martha had become ours -- our sometimes-annoying play-sister, our sweet-and-adoring daughter-we'd-never-had. Our family.

Over the years, AFS metropolitan Washington coordinator Chana Hays of the District has made 23 students from 10 countries -- including Japan, Hungary and Russia -- her family. (Students from Thailand, France, Brazil, Indonesia and Saudi Arabia are seeking Washington area families for the 2005-06 school year; for information, call 800-AFS-INFO.)

Hays says hosting a student provides families with a "sense of belonging to the world community -- and the ability as Americans to teach people about ourselves and themselves."

Like Helene and Martha, Hays believes it's about the learning, good and bad. Living in another country, "kids learn so much about themselves, what they're capable of," she says.

Most learn that they're not good, bad or even different.

They learn that they're family.