Background: Adolescent suicide is a public health issue, and school is an ideal setting for prevention activities. LEARN is a peer-led gatekeeper training for high school personnel, parents, and students. The purpose of this study was to evaluate the effectiveness of LEARN as a gatekeeper training. Methods: Paired t tests were used to compare pre- and post-training surveys for 4983 LEARN participants. Results: Participants reported an increased likelihood of engaging in each LEARN step: looking for signs, empathizing and listening, asking about suicide thoughts and plans, reducing danger, and connecting the person with help. Most participants were highly satisfied with the peer trainer's delivery of content. Conclusions: LEARN gatekeeper training was successfully implemented in high schools with students, parents, and school personnel. All groups reported increases in likelihood of approaching and providing support and connections for at-risk individuals and rated the trainer as effective, indicating satisfaction with the peer-led training format.