Update to the effectiveness and cost-effectiveness of a mindfulness training programme in schools compared with normal school provision (MYRIAD): study protocol for a randomised controlled trial. - Montero-Marin, Jesus; Nuthall, Elizabeth; Byford, Sarah; Crane, Catherine; Dalgleish, Tim; Ford, Tamsin; Ganguli, Poushali; Greenberg, Mark T.; Ukoumunne, Obioha C.; Viner, Russell M.; Williams, J. Mark G.; The MYRIAD team; et al. (Trials, 2021)