School-wide positive behavioral interventions and supports (SWPBIS) frameworks have been suggested as a promising approach to reducing disproportionality in school discipline practices; however, few studies have tested this potential, and findings have been mixed. In our sample of 27 urban schools and approximately 15,000 students, risk difference and ratio trajectories for office discipline referrals (ODRs) across 3 years of Tier I implementation evidenced sustained or, in some cases, heightened disproportionality for students identified as Black/African American or Latinx/Hispanic (relative to White; in a study subsample), identified as male (relative to a female), enrolled in each school's upper three grades (relative to lowest three grades), and not participating in special education (relative to participating in special education). Tier I implementation fidelity minimally contributed to expounding trajectories and outcomes across schools. These findings highlight the importance of equity-focused implementation and advanced-tier supports in the service of social justice within schools.