Magnet schools are one of the largest sectors of choice schools in the United States. In this study, we explored the heterogeneity in magnet-school effects on student achievement by examining 24 magnet schools, funded under the Magnet Schools Assistance Program (MSAP), in 5 school districts across 4 states. The magnet effects were synthesized across schools with a multilevel variance-known analysis, using the school-level effects estimated with a propensity score matched regression approach. Results indicated significant variation in magnet effects on student outcomes, with some magnet schools showing positive effects, and others showing negative effects. This variation can be explained by program implementation and magnet support.