Investigations of human potential and well-being recently have focused on mindfulness—a unique quality of consciousness that is defined as being aware of one’s thoughts and actions in the present moment. Previous research examining mindfulness among adults has found mindfulness to be positively related to indicators of well-being, such as optimism, positive affect, and self-regulation, and to be negatively related to indicators of maladjustment, such as depression and anxiety. Nonetheless, although much is known about the correlates of mindfulness in adult populations, the research examining mindfulness in children or adolescence is scant. The research is limited, in part, because of absence of measures that assess mindfulness in children and adolescents. The present investigation was designed to address this shortcoming by examining the reliability and validity of a modified version of the Mindful Attention Awareness Scale (MAAS)—a measure designed to assess mindfulness in adults. A total of 286 fourth to seventh grade children completed the modified version of the MAAS, the Mindful Attention Awareness Scale—Children (MAAS-C), as well as a battery of measures assessing a corpus of dimensions of well-being, including self-concept, optimism, positive and negative affect, school efficacy, classroom autonomy and supportiveness, depression, and anxiety. Results indicated that (1) the MAAS-C had high internal consistency (e.g., Cronbach’s alpha) and a one-factor solution, and (2) mindfulness, as assessed via the MAAS-C, was related in expected directions to indicators of well-being across the domains of traits and attributes, emotional disturbance, emotional well-being, and eudaimonic well-being. These findings were in accord with those of previous research with the MAAS in adult populations. Theoretical considerations regarding early adolescent development are discussed.