School effects on students' achievement are relatively small. Another approach, in which students' growth trajectories are the focal point of interest, is able to demonstrate more sizeable school effects. This approach is applied in a study into school compositional effects. The rationale of this study is that in Dutch primary education such compositional effects may not show up, because schools that have a disproportionate number of students from low socioeconomic families, especially if they are ethnic minorities, receive extra funding. The extra staff that they can hire should then at least counterbalance the negative school compositional effects. The study shows that growth of students is curvilinear, rather than linear, and that school effects on students' growth trajectories indeed are sizeable. School compositional effects could not be demonstrated, which might be interpreted in a positive way: The extra staffing may indeed counterbalance potential compositional effects. Implications of the findings are discussed. (Contains 2 notes, 5 tables and 2 figures.)