Examined are ecological attributes of the schools that preadolescents migrating from Puerto Rico to the United States (New Jersey) attend in this country during the first two years following their arrival (tf = 89 schools). The data show that Hispanics/Latinos are the majority of the student body in 43% of the schools; African Americans, in 30%; and European Americans, in 12%. Native speakers of Spanish are the majority of the student body in 29% of the schools. Approximately one half of the schools are located in economically depressed, highly urbanized areas. Although the schools are on average large, 44% of them enroll above capacity. In most schools the majority of the student body is from economically impoverished families with low levels of parental education. There are, however, wide differences among the schools on each of these variables. Correlations show that the higher a student body's proportion of Hispanics/Latinos or native speakers of Spanish, the higher is the student body's proportion of pupils from economically impoverished households with low levels of parental education, and the higher the school's likelihood of being crowded and of being located in a poor inner-city area. Similarly, the higher a student body's proportion of African Americans, the higher is the student body's proportion of pupils from low-income families, and the higher the school's likelihood of being in a poor inner-city area. Discussed are implications for policy and for students' academic, linquistlc, social, and emotional development; and hypotheses in need of research. Also presented is a historical overview, to the present, and discussion of U.S. policies and judicial decisions concerning school segregation.