Magnet schools have been criticized for intensifying the concentration of disadvantaged, low-achieving students at neighborhood high schools. This article investigates the impact of academically selective magnet high schools on the average achievement of ninth graders enrolling in neighborhood high schools in a large urban school district. The data from this district indicated that the composition of most of the lowest achieving neighborhood high schools is affected little by magnet schools because few students from these neighborhoods have the academic credentials to qualify for admission to magnet schools. In contrast, magnet schools have a greater effect on achievement at neighborhood high schools in high-achieving residence areas. Disbanding magnet schools would do little to remake the lowest achieving neighborhood high schools into viable institutions; instead, greater investments of human and financial capital, comprehensive school reform, and a long-term focus on ameliorating the underlying racial and class segregation of neighborhoods will be necessary.