Introduction: The objective is to design and analyze the psychometric properties of a new instrument, The Cognitive Reserve Questionnaire for Adolescents (CoRe-A), for assessing cognitive reserve in adolescents. Methods: A systematic review was conducted to identify cognitive reserve components, before items concerning them were discussed in terms of their suitability, relevance, and clarity. The final 12-item CoRe-A was subsequently validated among 48 adolescents diagnosed with severe mental disorders and 37 healthy controls matched by age and sex. Results: The CoRe-A scale showed a four-factor structure (i.e., education/occupation, sociability, school performance/development, and leisure activities) that explained 65.30% of the variance. It had adequate internal consistency (Cronbach's alpha coefficient = 0.767) and test-retest reliability (r = 0.979; p < 0.001). The patients with severe mental disorders obtained significantly lower scores than the healthy controls in both the total CoRe-A score and in the four factor scores. Moreover, the CoRe-A correctly classified 85.9% of the sample as patient with severe mental disorders or healthy control. The CoRe-A total score showed a large positive correlation with the Wechsler vocabulary subtest, demonstrating good convergent validity (r = 0.514; p < 0.001). Nevertheless, when vocabulary subtest and CoRe-A total score were compared, the CoRe-A reached a better discriminative capacity. Conclusions: The CoRe-A is a valid and reliable tool for assessing cognitive reserve in adolescents, and it may help to characterize adolescents diagnosed with a severe mental disorder. (c) 2022 SEP y SEPB. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).