The paper introduces a new multidimensional scale LA (lestvica agresivnosti [Aggression Scale]) for measuring self-reported aggression in elementary and upper secondary school students in Slovenia. The scale has been developed with a special focus on the school setting, using three elementary school samples (preliminary study: N=2777; main study: N=10427 and validity and test-retest study: N=191) representative of 4th and 8th grade students in Slovenia and one upper secondary school sample (N=3253) representative of the final year of upper secondary school in Slovenia. The exploratory analyses using principal component analyses (PCA) revealed a four-factor structure: verbal aggression, physical aggression, internal aggression and aggression towards authority that were interrelated. Confirmatory factor analyses (CFA) showed that the items of the scale formed four factors that were related to the higher order factor. The structure turned out to be stable over different age groups. The scale demonstrated adequate internal consistency, concurrent validity and test-retest stability.