Morning orientated students do better in school than evening orientated students (Preckel, Lipnevich, Schneider & Roberts, 2011). For elementary school children who in general are rather morning oriented (Roenneberg et al., 2007) there are only few findings. In the present study, we adapted the LOCI-questionnaire (Roberts, 1998) for parents' assessment of elementary-school childrens' chronotype and validated it in two independent samples (Ns=2718/216). Confirmatory factor analyses and structural equation modeling revealed (1) that morning and evening orientation were two separable factors of children`s chronotype, (2) that morning orientation was positively related to school-achievement, and (3) that this relation was completely mediated by childrens' academic self-perceptions. Our findings support the relevance of chronotype for learning and achievement in elementary school students.