When Ann Kahn was growing up, her family took the same summer vacation every year - a trip to Yosemite. But things are different for her daughter, Ashley.

At 19, Ashley has already set foot on every continent - including Antarctica. And all but one of her journeys abroad were taken without her parents, on trips with other teenagers. She started when she was just 13, visiting Europe with a youth travel organization called People to People Student Ambassadors (www.studentambassadors.org).

"It's definitely changed my life," said Ashley, a freshman at Sonoma State University. When she was younger, she thought she would like to be a nurse someday. But now, "I'm a French major. I'd like to work in an embassy. Living and working abroad is definitely something I would like to do."

Thousands of teenagers like Ashley are seeing more far-flung corners of the world, and at younger ages, than any previous generation of Americans. High schools now routinely organize student trips that require passports. Middle-schoolers hike the rain forest in Costa Rica instead of attending lakeside summer camps. And older teenagers use the community service they did in Africa as fodder for college essays.

A recent survey of 75 tour operators that belong to the Student Youth Travel Association (www.syta.org) found that the top 10 international destinations for youth travel include China, Peru, Brazil and Australia - along with the more traditional European destinations. More

"We still have the traditional tours: an eighth-grade trip to Washington or a high school trip to New York," association spokeswoman Debbie Gibb said. "But we're seeing growth in places like China that you never would have thought of 10 or 15 years ago. The world is shrinking, and the students who take these trips are getting younger."

Gibb said there are no reliable statistics on how many teens travel abroad compared to the past. But the travel bug is definitely going around. Teenagers today "want that notch on the belt," she said. "They want to say, 'I've been to Ghana.' "

Typically, these trips cost thousands of dollars. A 32-day trip to Europe offered by Westcoast Connection/360 Student Travel (www.westcoastconnection.com) is $9,399. A six-week program in Senegal sponsored by an outfit called Where There Be Dragons (www.wheretherebedragons.com) runs $7,300.

Westcoast Connection sends 1,500 teenagers each summer on a variety of tours, from language immersion to adventure and specialty sports like golf or snowboarding. But company spokesman Ira Solomon said, "There's definitely been a trend of more substantial summer programming. With colleges becoming so competitive, kids are trying to build their résumés."

So Westcoast also offers community service, sending kids to work in day care centers in shantytowns in Costa Rica, building houses with Habitat for Humanity in Hawaii and doing conservation work in an Alaskan rain forest.

Where There Be Dragons offers unusually intense six-week trips to China, Thailand, Cambodia, Vietnam, India, Guatemala, Peru, Bolivia, Senegal and Morocco, capping total enrollment at fewer than 300 students per summer to keep groups small. The trips include home stays, rugged travel, wilderness exploration, language study and learning about local culture, economy, art and religion.

As part of the Senegal trip, students live in a thatched-hut village for two weeks. "They thresh grain, draw water from the wells. They might do weaving or go out in the fields," said Chris Yager, founder of Where There Be Dragons. For a service project, one group brought in avocado and mango trees, then worked with villagers to figure out where to plant them, how to protect them from animals and how to distribute the produce. Students on the Senegal trips also get a goat to care for. At the end of their journey, they give the goat to a village to be slaughtered and eaten.

High school students have been taking summer courses on college campuses for decades. But Summer Discovery Pre-College Programs (http://summerfun.com) offers some of those classes for American teenagers abroad, at Cambridge University in England, University Politecnica Valencia in Spain and Instituto Lorenzo de Medici in Florence, Italy - in addition to programs at seven domestic campuses, from UCLA to Georgetown. The programs include language immersion and SAT prep as well as specialized subjects ranging from robotics to cooking.

Sometimes the pure fun of travel makes a bigger impact on kids than the educational aspects. Shana Jordan, 17, spent spring break this year in Italy with schoolmates from Stuart Country Day School in Princeton, N.J. But she expects to write her college essay not on Italian art and culture, but on two summer trips she took with ThrillCoaster Tours (www.thrillcoastertours.com) - visiting amusement parks.

"It's being able to do what every kid loves - but parents don't want to take them to do," she said. "You come for the coasters, but you love it for the friends who turn out to be like family. There's a whole world of coasters. But I also learned so much about myself."