This paper considers whether ethnicity is a social construction that is constantly being recreated in a nexus of shifting social relations rather than a set of perceptions and behaviors that remain constant and stem from a youth's membership in an ethnic group. Student responses about ethnicity from a larger study of student role and engagement in school provided impetus for this research, which used case studies of 10 students in urban high schools in California. The students, freshmen when the study began, include: (1) four Mexican American females; (2) two Vietnamese immigrant females; (3) two African American males; (4) one Italian American male; and (5) one Anglo American female. Semistructured interviews, school and classroom observations, and analyses of student records provide information about student experiences of ethnicity. The case studies support the view that what happens in schools does affect students' senses of themselves and their identities. The meaning of ethnicity is constantly renegotiated as students interact with teachers and peers in classrooms and at home. This research also suggests that teachers can work positively with youth who experience racism. There is a 29-item bibliography. (SLD)