LGBTQ youth frequently experience bullying and harassment in the school setting. Teachers are in an ideal position to prevent student harassment, yet most don't have adequate training. This study evaluated the effectiveness of "Step In Speak Up," an interactive online simulation. In a randomized controlled trial, 1390 participants received "Step In Speak Up" or no intervention. Participants were assessed pre- and post-intervention on the Gatekeeper Behavior Scale and attitudes toward the simulation. Results demonstrated significant differences (p < 0.001, multivariate ?[superscript 2 subscript partial = 0.17) between the training and control groups on learners preparedness, likelihood, and self-confidence in managing bullying behavior.