The Cognitive Telephone Screening Instrument (COGTEL) has shown to be a brief, reliable, and valid instrument to assess cognitive functioning in adults in face-to-face procedures as well as over the phone. So far, no psychometric evaluation exists on its use in adolescents. The present study set out to evaluate the psychometric properties of the face-to-face application of the COGTEL in adolescents in the school context and to analyse the association with school grades. We assessed cognitive performance using COGTEL in face-to-face assessments of 170 adolescents, with retests after 6 months for test-retest reliability. Predictive validity was assessed using school grades. Test-retest reliability for the COGTEL was good (ICC = .77; p < .001). The partial correlation controlling for age between COGTEL and school grades was medium and positive (r = .40; p < .001). School grades alone explained 42% and 36% of the variance in the COGTEL total score in elementary and secondary students, respectively. The present study suggests that COGTEL is a reliable and valid instrument to assess cognitive functioning in adolescents, with the advantage of feasibility in multiple contexts.