Suicide is a leading cause of death in adolescence. School provides an effective avenue both for reaching adolescents and for gatekeeper training. This enables gatekeepers to recognize and respond to at-risk students and is a meaningful focus for the provision of suicide prevention. This study provides the first systematic review on the effectiveness of school-based gatekeeper training in enhancing gatekeeper-related outcomes. A total of 815 studies were identified through four databases (Ovid Medline, Embase, PsycINFO and ERIC) using three groups of keywords: ‘school based’, ‘Suicide prevention programme’ and ‘Gatekeeper’. Fourteen of these studies were found to be adequate for inclusion in this systematic review. The improvement in gatekeepers’ knowledge; attitudes; self-efficacy; skills; and likelihood to intervene were found in most of the included studies. Evidence of achieving improvement in attitudes and gatekeeper behaviour was mixed. Most included studies were methodologically weak. Gatekeeper training appears to have the potential to change participants’ knowledge and skills in suicide prevention, but more studies of better quality are needed to determine its effectiveness in changing gatekeepers’ attitudes. There is also an urgent need to investigate how best improvements in knowledge and skills can be translated into behavioural change.