Jerry D. Weast, superintendent of Montgomery County schools, spent last week watching graduating seniors traverse stages to receive their diplomas -- including students who got their starts in Kenya, El Salvador, Vietnam, Iran and many other countries.

He watched the audience members as well.

"Sometimes you see an 'aha' in the crowd," Weast said, "the realization of what we've been saying all along: 'It's not coming. It's here.' "

"It" is the most racially and ethnically diverse graduating class the county has seen, and likely the last to be majority-white, according to school system data. Since the seniors graduating this month started kindergarten, the student body of Montgomery County public schools has grown larger by 16,000 Hispanics, 12,000 blacks, 7,000 Asians and 100 Native Americans. The number of non-Hispanic white students has declined by 3,000.

Minorities outnumbered white students in Montgomery's public schools for the first time in the 2000-01 school year. It's a shift occurring at various rates elsewhere in the Washington area, such as Prince William County, where the school system is 50 percent minority, and Fairfax County, where it is 47 percent minority.

"Diversity literally has turned many schools like Kennedy into a model United Nations," said Fred Lowenbach, principal of John F. Kennedy High School in Silver Spring, which went from about half minority in the mid-1980s to four-fifths minority now. "It has become a far more complex term to understand than 15 years ago, when it was just white-black. I just think it's kind of incredible."

As Montgomery County has grown more diverse in those 15 years, however, a smaller percentage of students are attending schools whose racial balance matches the county's in aggregate. The share of students attending public schools that are either predominantly white or predominantly minority has increased from 21 percent to 41 percent, according to a Washington Post analysis confirmed by a school system demographer. (A school is considered predominantly white or minority if its white or minority student percentage is at least 20 percentage points higher than the county total.)

Certainly, minority populations have increased at the vast majority of Montgomery schools. Of the county high schools in existence in 1988, the minority presence as a share of the population has increased at all but three: Walt Whitman in Bethesda, Poolesville and Bethesda-Chevy Chase.

But the county is still home to schools that have racial extremes: Broad Acres Elementary School in Silver Spring has three white students this year, for example, and Monocacy Elementary School in the northwest community of Dickerson has 31 minority students.

Most of Montgomery's black and Hispanic students are concentrated in the parts of the county where poverty is centered: a swath that stretches from Takoma Park up to Gaithersburg, primarily close to the Metrorail system. Those communities are home to slightly less than half of the county's elementary schools but, according to a study last fall, 78 percent of its Hispanic elementary schoolers and 71 percent of black elementary schoolers.

The school system has an official policy to promote pluralistic schools, part of which says, "The Board of Education is committed to the proposition that education is most effective in a diverse, integrated setting."

One way the county has done so is by offering special programs, such as technology and arts magnets, designed to draw white students into heavily minority schools. As well, school system officials said that part of the reason they offer certain communities a choice among several high schools is to improve racial balance. Since the school system was legally barred from using race as a factor in a school transfer program in 1999, and given the logistical complications, officials say they are left with few ways to make the racial mix of schools more proportionate.

Social scientists say that such balance helps children broaden experiences and avoid learning stereotypes. A diverse school is seen as both an opportunity to learn how to live in a global community or, for some, the only chance in a person's life to experience people from so many different ethnic and racial backgrounds.

Diversity in general is educationally valuable, said Maree Sneed, an education attorney in private practice who has represented Montgomery County schools and was a junior high school principal in Wheaton in the 1970s.

"If you're going to have a discussion about slavery with just African American students, it's going to be a different discussion than if you have it with African Americans and Hispanics and whites and Asians," she said. "They bring different viewpoints."

Then again, Sneed points out, a school can be diverse without having many white students, and officials say that even among whites there can be a broad range of children who are mixed-race, for example, or from immigrant families.

Evidence on whether the racial makeup of a school affects a student's academic achievement is scant, and much of what does exist is fairly inconclusive.

A study by Eric Hanushek, a senior fellow at the Hoover Institution of Stanford University, analyzed the test scores of every Texas fourth- through seventh-grader in the late 1990s. Factoring out school quality and family income, Hanushek found that the greater the black population of a school, the more it harms a black student's scores -- particularly a higher-achieving black student.

The study, however, found no effects of school composition on the performance of students from other racial or ethnic groups.

Weast said that whether a school is racially proportionate to the county doesn't matter academically. "I think the biggest divider isn't race, it's socioeconomics," he said, and along those lines he and county officials have pumped extra money into the county's poorest schools -- which, in general, tend to have higher minority populations.

Michael Durso, principal of Springbrook High School in Silver Spring, which like Kennedy has gone from half to one-fifth white, said students are students. Looking at a school's racial and ethnic composition doesn't tell much of story -- least of all to its students, he said.

"It's probably a concern much more to adults than to students," Durso said. "I've never had a student say to me, 'What's the percentage of Hispanic students?' "

Springbrook's population went from half to one-fifth white, which Principal Michael Durso says is more of interest to adults than students: "I've never had a student say to me, 'What's the percentage of Hispanic students?' "