ObjectivesThe Gaia program is a 12‐week mindfulness intervention based on cultivating body, emotional, and ecological self‐awareness, which has been shown to be effective in reducing children's and adolescents' internalizing problems at school. This paper presents the results of a cluster randomized controlled trial aimed at assessing the effectiveness of this program on improving psychological well‐being, subjective well‐being, and psychological distress in early adolescents.MethodsA sample of 195 early adolescent students (boys, n = 99; girls, n = 96) with a mean age of 11.49 years (standard deviation = 0.80) attending 12 middle school classes participated in the study. Seven Gaia instructors belonging to six schools led the program. Measures were administered at three time points, approximately every 3 months: 1 week before treatment, 1 week after treatment, and 3 months after treatment. We used a multilevel regression model to test whether treatment was effective in increasing psychological well‐being and subjective well‐being, and reducing psychological distress, as compared to a waiting‐list control group.ResultsThe results showed that the Gaia program improved psychological well‐being but not subjective well‐being and psychological distress. Specifically, the Gaia program was effective in increasing personal growth and purpose in life, the key eudaimonic components of psychological well‐being, in the experimental group whereas they decreased in the control group.ConclusionsFindings from this study provide preliminary evidence that the Gaia program for early adolescents may improve the core eudaimonic components of psychological well‐being from pretest to follow‐up that, conversely, decrease in the control group.