OBJECTIVE: Mindfulness-based interventions are increasingly being used in schools to improve students' mental, emotional, and behavioral development. Although many mindfulness programs exist, the types of programs that are effective for specific age groups remain unclear. In this systematic review, the authors used established rating criteria to describe the level of evidence for school-based mindfulness interventions. METHODS: A search of major databases, gray literature, and evidence base registries was conducted to identify studies published between 2008 and 2022 that focused on mindfulness interventions within school settings. The authors rated mindfulness interventions as having high, moderate, or low levels of evidence based on the number and rigor of studies with positive outcomes. RESULTS: Of the 24 interventions identified across 41 studies, three interventions-Learning to BREATHE, Mindfulness in School Project, and mindfulness-based stress reduction (MBSR)-received a rating of high level of evidence. Three interventions-Gaia Program, MindUP, and a blended version of MBSR and mindfulness-based cognitive therapy-received a rating of moderate level of evidence. The interventions rated as having a high level of evidence were conducted with middle or high school students, and interventions with moderate evidence were also conducted with elementary students, demonstrating effectiveness of mindfulness across a range of age groups. Few studies examined outcomes for underserved populations. CONCLUSIONS: With greater use and more research, mindfulness interventions have the potential to promote student well-being and prevent mental health conditions.