The current study addressed the need for experimental research on Restorative Practices (RP) in its evaluation of the Morningside Center for Teaching Social Responsibility’s Whole School RP Project. The study was conducted in a large Northeastern city using a cluster randomized controlled design in 18 elementary, middle, and high schools. In a single year, before the COVID-19 pandemic, and with data from 5,878 students, the study found that overall, students in the RP Project schools were less likely to receive a discipline incident record (11.1%) compared to students in the comparison schools (18.2%). However, differential treatment effects based on sex, race/ethnicity, and disability status were not found. The findings suggest prevention efforts are a cornerstone of practice/policy reforms to reduce the use of exclusionary discipline. Findings also suggest multi-year initiatives are needed to address discipline disparities.