Cognitive control, which involves the ability to pay attention and suppress interference, is important for learning and achievement during childhood. The white matter tracts related to control during childhood are not well known. We examined the relationship between white matter microstructure and cognitive control in 61 children aged 7–9 years using diffusion tensor imaging (DTI). This technique enables an in vivo characterization of microstructural properties of white matter based on properties of diffusion. Such properties include fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity, measures thought to reflect specific biological properties of white matter integrity. Our results suggest that children with higher estimates of white matter integrity in the corona radiata, superior longitudinal fasciculus, posterior thalamic radiation, and cerebral peduncle were more accurate during incongruent and neutral trials of a task of cognitive control. Importantly, less interference during the task was associated with greater white matter microstructure in the posterior thalamic radiation and cerebral peduncle. Fiber tracts in a frontal–parietal–striatal–motor circuit seem to play a role in cognitive control in children.