This study uses large-scale survey data and a multiple group, multilevel latent growth curve model to examine differential school effects between low, middle, and high social class composition public schools. The results show that the effects of school inputs and school practices on learning differ across the 3 subpopulations. Moreover, student learning in low social class schools is far more sensitive to school factors than in middle and high social class schools. Yet, even after controlling for an extensive set of student background characteristics and school inputs, students attending low social class schools continued to learn at significantly slower rates. Widespread differences in the characteristics of schools across the subpopulations, which consistently challenge the educational milieu in low social class schools, likely contribute to differential school effects, as well as to the disparity in learning rates. The findings of this study accentuate the importance of school effectiveness research that goes beyond generic models to examine differential effects. (Contains 1 figure, 3 tables, and 15 notes.)