Schools have a key role in promoting student social and emotional development and are encouraged to serve as a primary source of support, especially for those learners in need of special attention for addressing their needs. Young people's subjective emotional-social well-being is a general indicator of their mental health status. In this article, we present an assessment of the emotional, psychological and social well-being of Greek adolescent students, determine whether they are flourishing or languishing and investigate whether well-being varies by gender, age and year level. Analysis of data from over 500 Greek adolescent students (year levels 6-10) who completed the Mental Health Continuum (MHC) scale indicated that over half of the participants were flourishing, while only a small proportion were languishing and the remainder had moderate mental health. Gender differences were identified with female students reporting more challenges to their well-being than their male peers. Additionally, younger students were more likely to be flourishing than older students.