In a nation where most students learning English lag behind other groups by almost every measure, Hylton’s program stands out for its students’ high test scores and graduation rates. However, at this ordinary American high school, in an ordinary American suburb at a time of extraordinary upheaval, those achievements come with considerable costs.

The calm in the hallways belies resentments simmering among students who barely know one another. They readily label one another “stupid” or “racist.” The tensions have at times erupted into walkouts and cafeteria fights, including one in which immigrant students tore an American flag off the wall and black students responded by shouting, “Go back to your own country!”

Hylton’s faculty has been torn over how to educate its immigrant population. Some say the students are unfairly coddled and should be forced more quickly into the mainstream. And even those who support segregating students admit to soul-searching over whether the program serves the school’s needs at the expense of immigrant students, who are relentlessly drilled and tutored on material that appears on state tests but get rare exposure to the kinds of courses, demands or experiences that might better prepare them to move up in American society.

“This is hard for us,” said Carolyn Custard, Hylton’s principal. “I’m not completely convinced we’re right. I don’t want them to be separated, but at the same time, I want them to succeed.”

Education officials classify some 5.1 million students in the United States — 1 in 10 of all those enrolled in public schools — as English language learners, a 60 percent increase from 1995 to 2005.

Researchers give many causes for the gaps between them and other groups. Perhaps most paradoxical, they say, is that a nation that prides itself on being a melting pot has yet to reach agreement on the best way to teach immigrant students.

In recent years, students learning English have flooded into small towns and suburban school districts that have little experience with international diversity. Meanwhile, teachers and administrators have come under increasing pressure to meet the requirements of the federal No Child Left Behind Act, which links every school’s financing and its teachers’ jobs to student performance on standardized tests.