Research has shown that thinking styles could have an influence on academic achievement. Previous studies have described that evening types are usually right-thinkers who tend to be creative and intuitive, whereas morning types tend to be left-thinkers who prefer verbal and analytic strategies in processing information. However, these studies have been realized among undergraduates, who have more freedom to choose their time schedules according to their circadian preference than adolescents or adult workers. On other hand, the relationship between thinking styles and circadian preference has not been analyzed considering school achievement. The present study aims (1) to investigate the relationship between circadian preference, that is, behavioral differences in circadian rhythmic expression, and thinking styles, referring to the preference toward information processing typical of the right versus the left cerebral hemisphere; and (2) to test the implications for self-reported school achievement. A sample of 1134 preadolescents and adolescents (581 girls; mean ± SD age: 12.1 ± 1.47, range: 10-14 yrs) completed the Morningness-Eveningness Scale for Children (MESC) as measure of circadian preference (morning, neither, or evening types), the Hemispheric Preference Test (HPT), conceived as a tool to measure thinking styles (right-, balanced-, and left-thinkers), and self-reported school achievement. Results indicated a greater percentage of left-thinkers among morning types and a greater percentage of right-thinkers among evening types. No differences were found among balanced-thinkers and neither types. Morning types and left-thinkers reported the highest subjective level of achievement, followed by evening types and left-thinkers, and morning types and right-thinkers. Evening types and right-thinkers reported the lowest subjective level of achievement. Finally, multivariate regression analysis indicated that age, left hemisphere and morning preferences accounted for 14.2% of total variance on self-reported achievement.