Dispute resolution institutions facilitate agreements and preserve the peace whenever property rights are imperfect. In weak states, strengthening formal institutions can take decades, and so state and aid interventions also try to shape informal practices and norms governing disputes. Their goal is to improve bargaining and commitment, thus limiting disputes and violence. Mass education campaigns that promote alternative dispute resolution (ADR) are common examples of these interventions. We studied the short-term impacts of one such campaign in Liberia, where property disputes are endemic. Residents of 86 of 246 towns randomly received training in ADR practices and norms; this training reached 15% of adults. One year later, treated towns had higher resolution of land disputes and lower violence. Impacts spilled over to untrained residents. We also saw unintended consequences: more extrajudicial punishment and (weakly) more nonviolent disagreements. Results imply that mass education can change high-stakes behaviors, and improving informal bargaining and enforcement behavior can promote order in weak states.