SALINAS, California - A girl in Oscar Ramos’s third-grade class has trouble doing homework because six relatives have moved into her family’s rusted trailer. A boy confides, “Teacher, on Saturday the cops came and took my brother.”

At Sherwood Elementary here, Mr. Ramos, 37, glimpses life beneath the field dust. His students are the children of the seasonal farmworkers who toil in the vast fields of the Salinas Valley.

One-third of the children are migrants whose parents follow the lettuce from November to April, Salinas to Yuma, Arizona. Some who leave will not return.

“Dear Mr. Ramos,” they write, “I hope you will remember me. . . .” Mr. Ramos, the child of migrants himself, always does.

Schools like Sherwood struggle against family mobility, neighborhood violence and a mentality of low academic expectations. But the often disrupted lives of the children of migrants here is likely to grow still more complicated as the national debate over immigration grows sharper.

Despite a ruling by the United States Supreme Court that every child is entitled to a public education, efforts by lawmakers to rescind citizenship for children born in the United States to illegal immigrants and ban them from schools are already stoking fears among many agricultural workers. Some parents, as they move with the crops, are already keeping their children out of school when they get to Arizona because they are worried about the bureaucracy and tougher restrictions in the state.

At Sherwood, 97 percent of students are near the poverty line, compared with 56 percent statewide. Seventy- seven percent have limited English, versus 32 percent throughout California. Only 6 percent of parents here attended college - the state average is 55 percent - and many are illiterate in their native language.

Sherwood hovers near the bottom of the state’s performance index, along with more than 100 California elementary schools with a similar demographic, many in the agricultural strongholds of the San Joaquin and Salinas Valleys.

Even as Latino enrollments grow, the number of new teachers earning bilingual credentials has fallen. The shortage of bilingual teachers is hurting Latino academic achievement, said Bruce Fuller, a professor of education and public policy at the University of California, Berkeley. Teachers like Mr. Ramos, “who have both language skills and the framework to respond to these kids’ cultural assets,” Professor Fuller said, are all too rare.

Sherwood sits on a fault line of violence between two rival street gangs; a first grader was wounded by gunfire last year. Bruce Becker, Sherwood’s violence prevention specialist, counsels students who sleep beneath carports and live in such cramped quarters that their parents take them to the local truck stop to wash up before school. Jose Gil, a high school teacher, said many of his students did not see much of their parents during harvest season.

“They have little brothers and sisters to take care of, ” he said. “Yet they’re supposed to turn in a 10-page paper by tomorrow? ”

Recent crackdowns at the border have meant longer family separations. “My mom’s in Mexico with my little baby sister,” says one girl in Mr. Ramos’s class. “Every day she calls me, but some days she forgets.”

The $394 million federal Migrant Education Program provides health care, summer school and tutoring for migrant children. Still, nearly half do not complete high school. California has about 200,000 children in the program, one-third of the national total.

There are signs of progress in Room 21: last year, 13 students moved up a level in math, surpassing the state average.

Sherwood’s migrant student population dropped 10 percent last year, in part, said Rosa E. Coronado, the migrant education director for Monterey County, because “parents are getting the message that it’s not beneficial for the children to move around .”

Still, one boy in Mr. Ramos’s class did not attend school for five months. This year, his father will move for work. But his mother will stay in Salinas, worried, she said, that “my son is falling behind.”

By PATRICIA LEIGH BROWN