Although student well-being and mental health are government-identified responsibilities for New Zealand schools, the extent to which school-based well-being and mental health interventions are currently delivered is unknown. This survey of a nationally representative sample of schools was undertaken to identify: what well-being and mental health interventions are currently used by primary (elementary) and secondary (high) schools; what gaps exist between current practice and the evidence base; what ideas staff have for improving student well-being and mental health; and what barriers staff can identify for implementing evidence-based interventions and suggestions for how these may be overcome. Forty staff from 37 (22 primary, 13 secondary and 2 composite) schools participated in semi-structured interviews. Seven key themes were identified: (1) awareness and enthusiasm about student well-being and mental health; (2) existence of specific interventions to support student well-being and mental health; (3) support for government-sponsored programmes; (4) limitations of existing programmes; (5) drivers of new interventions; (6) perceived barriers to the implementation of new interventions; and (7) suggestions for future interventions and their implementation. Currently, a wide range of primarily non-evidence based well-being and mental health interventions are delivered in a variable manner by school-based and external providers. Despite current enthusiasm by schools, there is room for improvement in the quality and equity of intervention delivery.