Partnerships between teachers and parents from nondominant communities hold promise for reducing race- and class-based educational disparities, but the ways families and teachers work together often fall short of delivering systemic change. Racialized institutional scripts provide "taken-for-granted" norms, expectations, and assumptions that constrain marginalized families and educators in exercising collective agency to disrupt educational inequities. In this paper, we bring together the concept of institutional scripts from organizational theory with transformative agency from sociocultural learning theories to address the moment-to-moment interactions between families and educators that may rewrite racialized institutional scripts and expand collective parent-teacher identities. Drawing examples from a parent-educator participatory design-based research project, we highlight how collaborative activity might (a) reframe expertise, (b) surface and examine contradictions, and (c) attend to power in relational dynamics in order to expand identities and interactions in the presence of racial, cultural, and class differences across roles. We argue that examining parent-teacher activity through these lenses opens possibilities for building parent-teacher relations toward collective agency and critical solidarities toward educational justice.