Noncontiguous school attendance zone boundaries (AZBs) have a unique, relatively uncommon shape that assign two or more non-adjacent residential areas to the same school. Given their ability to shape school enrollments by taking advantage of residential sorting, noncontiguous AZBs have historically been linked to explicit efforts to both segregate and desegregate schools. In this paper, we use a novel, longitudinal dataset of AZBs and descriptive quantitative and geospatial methods to understand how the relationship between noncontiguous zones, school diversity, and neighborhood demographics changed from 1990-2020 in two southwestern school districts--Tucson Unified School District, Arizona and Fort Bend Independent School District, Texas. Each district has a unique legal history and demographic context that informs their use of noncontiguous AZBs. We find noncontiguous AZBs are more strongly associated with racially diverse schools and are more likely to bring together neighborhoods with different compositions in Tucson compared to Fort Bend. However, the association between Tucson's noncontiguous AZBs and racially diverse schools has waned since 1990, as the district has negotiated the end of its court-ordered desegregation plan. Our findings provide insight into when and how noncontiguous AZBs can effectively contribute to ethnoracially diverse schools.