Recently, the largest test of a school-based mindfulness programme to date, the My Resilience In Adolescence (MYRIAD) trial, found that participating in weekly mindfulness lessons did not improve students’ well-being compared to teaching as usual, with low uptake of recommended home mindfulness practice. One potential explanation for the null result and low uptake is that adolescents might be unlikely to adhere to home mindfulness practice recommendations when choosing between mindfulness and their graded homework or more stimulating activities. Indeed, many studies of school-based mindfulness programmes have reported low adherence to home practice recommendations. Home practice recommendations also create equity issues, as many students may find it difficult to make the time for home mindfulness practice, a factor that is more likely to affect students who are disadvantaged. As such, we argue in this article that research needs to test whether school-based mindfulness programmes that make mindfulness practice time available in the school day result in higher adherence to mindfulness practice recommendations, and whether these programmes are effective at improving student mental health. Unfortunately, very little research has examined how much mindfulness practice is required to obtain meaningful effects. We summarise the small volume of mindfulness dose-response literature to provide guidelines for how much school-based mindfulness practice might be sufficient and provide suggestions for further testing. While making mindfulness practice time available in the school day may be difficult to implement, its efficacy is currently untested. Youth mental health remains a critical issue, providing strong justification for testing whether mindfulness practice made available in the school day results in better outcomes, despite the challenges posed in pursuing this research avenue.