THE Boston junior-high-school student says he often can't remember the teachers or students from his last school. ''I forget what it looks like,'' says the boy, who is now attending his 12th school in the last three years.
Another boy, who arrived midyear at a school in nearby Somerville, Mass., pulled a coat over his head for the first six weeks and refused to participate. He was at his 15th school in three years.
Americans once held the ideal of a student attending the same neighborhood school from kindergarten through elementary grades.
But high student mobility has become a daunting reality of the nation's urban schools. And it is prompting a fundamental shift in learning as urban teachers and administrators struggle to accommodate revolving-door students, educators say. Not only are teachers finding it more difficult to build a cohesive unit in the classroom, but they are increasingly forced to teach a less-demanding curriculum.
Triggering the changes are three main forces: economic pressures on low-income families who are on the move to find low-cost housing; the instability of many of these families; and a lack of parental investment in schools, which they often distrust.
Add a high rate of turnover of principals and teachers in urban schools, says Scott Miller, the author of a report on student mobility for the Council for Aid to Education in New York, ''and the problem of mobility is simply one layer in a much bigger onion of problems.''
A 1994 Government Accounting Office (GAO) report stated that 1 in 6 of the nation's third-graders - over half a million - has attended three schools since the first grade. At urban schools, the figure is often double that.
The signs of movement can be found everywhere:
In Elizabeth, N.J., 98 percent of the children at Public School 2 had spent part of the year somewhere else, according to a 1993 state Department of Education report. At another school in Jersey City, the rate was 89 percent.
In Montgomery County in Maryland, the percentage of all students who have attended at least two schools in an academic year has risen to 24 percent today from 12.9 in l983.
And in Florida, where the statewide mobility rate is 37 percent, one elementary school in Osceola County had a rate of 84 percent in l994.
In classrooms, as students come and go, the consequence is often a shift to more review of material. Introduction of new topics is much slower. Transfer of students' records is often so slow that teachers have no background on new students for weeks. And teachers and administrators cannot evaluate the effectiveness of what they are doing because much of the evidence continually leaves the school.
''Across the grades what happens is a flattening of the curriculum,'' says David Kerbow, a research associate at the Center for the Study of Students Placed at Risk jointly run by Johns Hopkins University in Baltimore and Howard University in Washington. ''The impact on stable students means their exposure to new material is reduced, and over time exposure to ideas and concepts is very closely related to achievement,'' says Mr. Kerbow, who is conducting a five-year study on mobility in Chicago for the US Department of Education. ''An unstable classroom reduces the opportunity to learn.''
And children who change schools frequently are more prone to dropping out, says Richard Weissbourd, author of ''The Vulnerable Child; What Really Hurts America's Children and What We Can Do About It.''
''The chance increases 2.6 percent with each move,'' he says. ''A hundred years ago, people moved a lot, but usually to be with other family members, and they were absorbed quite well. Today, people move for different reasons: for jobs, for housing - and this is on top of family and community instability.''
To minimize the mobility problem, a few schools are working toward solutions that zero in on some of the underlying causes.
At Holbrook Elementary school in Houston, the mobility rate is 50 percent. But the multitrack campus operates year-round and allows students to take remedial classes anytime, thus helping to avoid disruption in their regular classroom. ''Children who are very mobile can do some catching up,'' says assistant principal Robert Borneman.
Spry Elementary School in Chicago, which serves a predominantly Hispanic inner-city community, cut its more than 35 percent mobility rate by 20 percent between 1991 and l994. Overcrowded, and with extremely low test scores, only 9 to 10 percent of Spry's students scored at or above grade level.
But under new principal Carlos Azcoitia, and a school council of six parents and two community members, the school started a reform effort by relieving overcrowding with classrooms rented from other organizations.
Day care and classes including English, were offered for parents. In the community, issues of safety were addressed with the police. A full-time nurse was hired, along with a social worker. Parent leaders were identified in blocks around the school, and held meetings at night about literacy, critical thinking, and responsibility.
''What happened was that our council meetings suddenly had 80 and 90 people in attendance,'' says Mr. Azcoitia, now the director of school and community relations for Chicago Public Schools.
Inside the classroom, the percentage of students reading at or above grade level grew to 20 percent. Most important, while parents continue to move their families, more are staying within the boundaries of the Spry area to avoid having to change schools.