Purpose This study examines notions of sustainability in professional development schools (PDSs) through a critical, project-based (CPB) clinical model that challenges conventional concepts of sustainability in school–university partnerships (SUPs). Rather than focusing on structural SUP elements like formalized agreements or stable funding, the authors explore sustainability as an iterative process enacted through boundary-spanning activities that prioritize impact and mutual benefit for all participants. To this end, the authors propose a series of metaphors that help reconceptualize these more responsive PDS models. Design/methodology/approach This multiple case study analyzed qualitative data from four preservice teacher/school-based teacher educator pairs participating in the secondary education “Problems of Practice” CPB clinical experience. Examined through thematic analyses, data sources included pre-/post-surveys, observation logs, and interviews with eight participants. Findings Three key themes emerged: mutual growth, mutual goals, and relationship-based mentor selection. In the discussion, we examine these themes – alongside formalized “Essentials” of PDS sustainability – to propose illustrative metaphors for PDS sustainability. Originality/value This study reconceptualizes PDS sustainability by challenging intensification and scalability as primary metrics, instead emphasizing responsive, relationship-based interventions. While not discrediting other PDS formats, the CPB model offers an alternative pathway to sustainable partnerships that honors educators' authentic needs while resisting neoliberal demands for replicability and standardization that often undermine boundary-spanning collaboration. Recognizing the potential of metaphors to crystalize complex ideas, the authors propose analogies to guide the development of novel PDS initiatives and better communicate with diverse partners.
Rudder et al. (Sun,) studied this question.