This longitudinal study (three waves across a school year) investigated the links between children's motivations to respond without prejudice and their ethnic outgroup attitudes at the between-person level (means and changes over time) and the within-person level (time-specific fluctuations). Participants were 945 ethnic majority students (MageW1 = 9.86 years, SD = 1.21; 471 girls) from 51 grade 3-6 classrooms in the Netherlands. Children reported (increasingly) more positive outgroup attitudes when their internal motivation was structurally high (between-person effects) and temporarily high (within-person effect), and less positive attitudes when their external motivation was structurally and temporarily high. The between-person effects were independent of the ethnic composition and the antiprejudice climate of the classroom. These findings may help in developing interventions aimed at reducing prejudice in late childhood. (PsycInfo Database Record (c) 2023 APA, all rights reserved).