This study verified the effects of a Mindfulness and Social-Emotional Learning Program (M-SEL) in mental health problems and quality of life (QoL) in fifth graders of elementary public schools in Southern Brazil. A total of 132 students with a mean age of 11.1 (SD = 1.19) years old were selected. Students (n = 64) who received up to 12 M-SEL sessions during 5 months were compared with a wait-list control group (n = 68). Intervention combined mindfulness practices, Collaborative for Academic, Social, and Emotional Learning competencies, and the council method. Outcomes were measured by the Strengths and Difficulties Questionnaire (Fleitlich, Cortazar, & Goodman, 2000), the Youth Quality of Life Instrument (Salum et al., 2012), and the Swanson, Nolan and Pelham-IV (Mattos, Serra-Pinheiro, Rohde, & Pinto, 2006) questionnaire. Relative to controls, M-SEL participants significantly improved in most mental health domains (emotional, conduct, relationship, and prosocial behavior) and in QoL scores. No changes occurred for attention deficit and hyperactivity symptoms. These preliminary results suggest the potential psychological contribution of the M-SEL program, as well as its feasibility as a psychosocial intervention for Brazil’s educational system.