This study investigates school effects on primary school students' language and mathematics achievement trajectories in Chile, a context of particular interest given its large between-school variability in educational outcomes. The sample features an accelerated longitudinal design (3 time points, 4 cohorts) together spanning Grades 3 to 8 (n = 19,704 students in 156 schools). The magnitudes of school effects on students' growth trajectories were found to be sizeable (generally larger than school effects in Western industrialised countries) and moderately consistent across school subjects. School composition effects on student achievement status were found for both school subjects. However, there was no evidence of composition effects on student achievement growth. The study provides new evidence on the size and nature of school effects in a developing country context based on state-of-the-art methods (i.e., accelerated longitudinal and growth curve models).