Over the last decade, there has been a growing interest in mental health literacy (MHL) in health promotion, largely motivated by increased awareness of MHL as a modifiable determinant of mental health. Accordingly, MHL has been associated with the health-promoting school approach emerging over the last 20 years. To succeed in promoting MHL, it is of vast importance to evaluate working strategies and interventions to address MHL using validated instruments. The current study describes the revision and psychometric testing of a modified version of the 10-item adolescents’ positive MHL measure, the MHPK-10, the only identified instrument measuring adolescents’ positive MHL. The MHPK-10 was adjusted to address the previously documented ceiling effects and was further optimized for use in schools by reworking it to measure learning rather than self-reported knowledge, becoming the new nine-item Mental Health Learning Scale (MHLS-9). The MHLS-9 was tested on a national sample of N = 2,012 Norwegian ninth graders. Data were analyzed by confirmatory factor analysis (CFA) and tests of reliability and validity. The revised CFA model for the MHLS-9 showed an improved fit over the original CFA model for the MHPK-10. The MHLS-9s’ CFA model revealed excellent factor determinacy (.95) and scale reliability (ω = .91). Thus, the MHLS-9 is an improved measure for the positive component of MHL for use in school settings, enabling researchers and practitioners to evaluate and focus positive MHL interventions in schools using a short, reliable, and valid measure for adolescents’ learning about the factors promoting good mental health.