The sprawling mass of teenage humanity that calls itself Robinson Secondary School, the largest high school in the Washington area -- with more than 4,000 bodies -- overwhelmed Marco Garces when he arrived four years ago from a 400-student private school in Richmond.

"The first week, I just felt lost all the time," the 17-year-old senior said of the Fairfax County school. "I didn't know where I was."

But now, he said, he loves the noise and clamor at lunchtime and between classes. "There is always something going on," he said, "and you always have someone to hang out with."

As states, school systems and private groups, backed by donations from software magnate Bill Gates, put new emphasis on making high schools smaller, monster campuses such as Robinson increasingly look out of place. Yet many of the educators who run them say big is not always bad and point to an array of unusual opportunities that large schools provide students.

"The fact that our school is so large allows us to offer a wide variety of electives that we may not be able to offer otherwise," said Shawn Ashley, principal of Long Beach Polytechnic High School in California, which has 4,779 students in ninth through 12th grades. Long Beach Poly's electives include print shop, auto shop, drafting, electronics, six kinds of art, nine science courses and many music choices.

Robinson, which has seventh through 12th grades, offers much of the same, including seven classes in ceramics, seven in guitar, a jewelry making class and one devoted to Shakespeare. The 60-acre campus on Sideburn Road just south of George Mason University has 491,219 square feet in a seemingly endless two-story building of light brown brick with blue trim. There are nearly 500 teachers and staff members, 300 sinks, 196 toilets, 58 buses and more than 70 student organizations, including the Bowling Club, the Muslim Student Association, the Improvisation Club and the Korean Drumming Club.

"We have a great majority of good kids here," Robinson Principal Dan Meier said. "And thank goodness, because there are so many of them."

But as in much of American public education, big schools in affluent suburbs such as Fairfax County are very different from big schools in low-income neighborhoods, where parents cannot give as much support and good teachers are harder to find. Eight of the 10 largest public schools in the country are in the Los Angeles Unified School District, and in most cases those schools are full of students from poor and minority families, and severely overcrowded.

Garfield High School in East Los Angeles, for instance, is populated almost entirely by the children of low-income Hispanic residents. In 1988, when its Advanced Placement calculus teacher Jaime Escalante was made famous by the film "Stand and Deliver," Garfield was already a large school with 3,500 students; it now has nearly 5,000. It must put its students on three vacation schedules so no more than two-thirds of them are on campus at the same time.

"They neglected building any high schools here for 30 years," said Los Angeles School Superintendent Roy Romer, a former Colorado governor. He has won voter approval for a massive $19 billion construction and renovation program, designed to add 180,000 classroom seats in the next nine years and eliminate the tracked schedules.

Romer said that will still leave some high schools with 3,500 students. The larger size, he said, helps schools pool resources for athletics, food service and advanced courses, but "we've got to lean toward smaller schools." To do that, Los Angeles will join other urban school systems in breaking schools into what are called smaller learning communities, where students have regular contact with a small group of teachers. Gates's money and other efforts to reduce high school size are based on research showing that students learn more and are more likely to stay in smaller schools where they feel teachers know and appreciate them.

In some ultra-large suburban high schools, however, students, parents and teachers have grown accustomed to the wide choice of classes, the noisy bustle before and after school and at lunch, and they don't want to change.

"Some people absolutely thrive in large schools," said Ashley, the Long Beach Poly principal. "It is like New York City. Some students like being a part of something that is bigger than themselves."

Doyle Dean, principal of Plano Senior High School near Dallas, said his students don't appear to be getting lost in the crowd, even though he has 2,563 in two grades, 11th and 12th. "Our participation rate of over 80 percent in competitive and noncompetitive activities compares favorably with smaller schools," he said.

New Trier High School in Winnetka, Ill., near Chicago has 3,070 students on one campus for 10th through 12th grades and a separate campus with 1,024 freshmen, but few parents or students complain about the size. "Our ability to construct a student's optimal schedule of classes is maximized because more teachers are available for assignment in a given class period in a large school," said Hank Bangser, superintendent of the New Trier Township High School District.

At Robinson, Garces said he likes the array of classes and activities. He is active in DECA, a club for students interested in marketing and entrepreneurship. The Robinson DECA club has won several international marketing competitions, and Garces raved about the opportunities it had opened for him.

Katie Planert, an 18-year-old senior, said she is also active in DECA and other activities. That allows her to overlook the annoyances of getting around the school. Where she stood, next to the junior and senior class lockers, "sometimes you can't move five feet in five minutes," she said, but otherwise she is glad to be there.

Meier said he and his large staff keep students and parents happy by emphasizing challenging academic classes, such as those in the International Baccalaureate program, which is the largest in the country. Recognition for acts of kindness and hard work, such as awards for student of the quarter and teacher of the quarter, also improve the mood, he said. At the last quarterly award ceremony, Meier said, many students praised teachers for making the big school "feel like home."

Meier said big schools do better in sports because they have so much talent but also make it hard for students to participate in more than one sport because of the demands of high-level competition. The same goes for drama and music.

So, he said, he has to think about ways to make a big school feel small. "You really work at trying to do as many things as you can to recognize the individual," he said.

Some of Robinson Secondary School's more than 4,000 students flood a hall between classes. The Fairfax campus comprises seventh through 12th grades.