Bold interventions are needed to change racial disparities and unacceptably low STEMM completion rates at historically white institutions that have the resources to train a new generation of scientists with diverse backgrounds. Three university case studies were conducted on the Meyerhoff Adaptation Partnership, which sought to develop student-centered programs to improve student outcomes and change STEMM institutional cultures. We employ an institutionally-focused approach to examine how the collaboration facilitated the development and mutual learning of equity-minded schemas to challenge dominant racial logic that stifles diversity, equity, and inclusion in STEMM. The study expounds on how dialogic cross-institutional mentoring works, including how participants learned from each other at multiple levels across institutions to advance fundamental values and practices that hold promise for inclusive approaches in STEMM. The study shows how mentoring relationships support change agents in implementing, sustaining, and institutionalizing STEMM interventions that seek to advance diversity, equity, and inclusion on their campuses. Discussed is the value of the cross-institutional mentoring model to share and co-create innovative strategies, expand professional development for institutional agents, affirm change agents, and overcome program challenges.