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 (M[subscript ageW1] = 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.