The role of principal supervisor has been shifting from a focus on management to one that emphasizes support for principals. External partners can sometimes help with redesigning the role and other aspects of district organization. However, most research focuses on large urban districts with role conceptions and organizational structures that are not easily applied to midsized districts. In this study, we leverage contingency theory as a way to consider how contextual difference might matter in the use of principal supervisors to support and develop principals of underperforming schools. We interviewed district superintendents, principal supervisors, and principals in five mid-sized districts partnered with USSP, an in-service educational systems leadership provider with research evidence of impact on student achievement outcomes. We found that mid-sized districts commonly prioritized characteristics and traits regularly associated with good principal supervisors, but they were limited by district size and context in how they could initiate change. Despite some differences in how districts established the principal supervisor role, participants across levels described how principal supervisors were supported and, in turn, supported principals in intensive ways. Study results suggest that reorienting the principal supervisor's role, even in mid-sized districts, can build leadership capacity of principals leading underperforming schools.