This paper presents an overview of a 3-year, federally funded comparative study of 11 public school districts and 40 schools in metropolitan areas of California, Arizona, and Nevada. The purpose was to identify school districts that are successfully meeting the challenge of educating relatively high numbers of newcomer students (ethnic and language minorities and immigrants), to compare these districts systematically with less successful districts, and to search for models of success that might be shared. The communities were heavily affected by ethnic and language minority students in the 1980s, and differed markedly in their achievement-gain scores. Examination of their histories and local cultures led the research team to conclude that score differences were not the result of chance. There were three communities with proactive, responsive, adaptive, and innovative public instruction, and eight in more or less severe states of confusion and inefficiency. Superintendents who succeeded regarded cultural diversity as a strength of their schools. The evidence suggests that schools and districts can help to lift or to depress student-learning outcomes. The study supports current research literature in suggesting that very large districts have a difficult time succeeding if they contain large numbers of very disadvantaged students. (Contains 2 references.) (SLD)