<p>This exploratory study examined the impact of the newly developed Mindful Breathing Program (MBP), a grassroots mindfulness-based intervention, on the social-emotional well-being of students and teachers in a K–12 public school district in the United States. Pre- and post-intervention measures assessed students’ levels of mindfulness, affect, social-emotional functioning, and prosocial behavior, as well as teachers’ mindfulness traits and embodiment of mindfulness in instructional practice. Results indicated that students demonstrated increases in mindfulness, positive affect, and prosocial behaviors, along with reductions in negative affect, emotional symptoms, hyperactivity/inattention, and conduct problems. Teachers also showed significant gains in acting with awareness, describing and accepting inner experiences, nonreactivity, and mindful engagement in teaching, as well as increased self-efficacy for managing stress, supporting student behavior, and using responsive instruction. Overall, findings suggest that participation in MBP supports self-regulation, emotional balance, and well-being among both students and educators. Findings are discussed in terms of emphasizing contextual fit, relational connection, and local stakeholder engagement for developing and using mindfulness-based programs such as MBP.</p>