STERLING, Va. — Some 55 million youngsters are enrolling for classes in the nation’s schools this fall, making this the largest group of students in America’s history and, in ethnic terms, the most dazzlingly diverse since waves of European immigrants washed through the public schools a century ago.

Millions of baby boomers and foreign-born parents are enrolling their children, sending a demographic bulge through the schools that is driving a surge in classroom construction. It is also causing thousands of districts to hire additional qualified teachers at a time when the Bush administration is trying to increase teacher qualifications across the board. Many school systems have begun recruiting overseas for instructors in hard-to-staff subjects like special education and advanced math.

The rising enrollments are most obvious in districts like this one west of Washington, in Loudoun County, one of the nation’s fastest-growing school systems. Thousands of government, technology and construction workers, many of them Hispanic, Asian and African-American, are streaming into new subdivisions within commuting distance of the Pentagon and the headquarters of America Online. They are transforming a school system that was once small and overwhelmingly white into one that is sprawling and increasingly cosmopolitan.

Thuy Nguyen, a 16-year-old junior at Park View High School in Sterling, has watched the recent transformation. She moved with her family to Virginia from Vietnam when she was 9 years old, and recalls that most of her fifth-grade classmates were white.

"I was new, afraid, and I didn’t speak very well English," Nguyen said. "I didn’t talk to anybody." Six years later she says making friends is easier.

"What I like about a diverse school is that you don’t feel intimidated if there are other races," she said. "I’m jumping around, talking to the Caucasian clique and the Middle Eastern clique. I have friends from El Salvador, Mexico, Peru — one girl is half Korean and half Puerto Rican, she’s cool — and from India, Pakistan, Afghanistan.

"There’s a girl from Bangladesh; we tell each other everything. I also knew a Swedish guy. He happened to be very hot. So I talk to all the different groups. I don’t want it to be, like, ‘You’re just in the Asian clique.’"

Kathy Hackney is Nguyen’s tennis coach.

"My team looks like the League of Nations," Hackney said.