This report explores how grantmakers can help strengthen collaborations among supported groups to advance ambitious social change goals. As noted by Grantmakers for Effective Organizations in Many Hands, More Impact, grantmakers can play a number of critically important roles in supporting social movement building: investing in a broad range of organizations, change strategies, and issues; brokering relationships among groups and their allies; connecting grantees to one another in impactful ways; fostering learning to grow a field; and influencing peers and policy through these supports. We focus on grantmakers' "connector" role because we see it as a crucial -- and often underexamined -- strategyfor expanding impact. But how, specifically, can grantmakers nurture connections -- and productive collaborations that may eventually arise from them -- while remaining attuned to the strategic intentions of supported groups and the relationships they themselves want to cultivate? And how can the enhanced capacity that genuine collaboration requires be reflected and resourced in ways that meet funders' expectations of collaborative impact? Our perspective on these questions is grounded in the experience of Communities for Public Education Reform (also referred to here on as "CPER" or the "Fund"). CPER is a national funders' collaborative committed to improving educational opportunities and outcomes for students -- in particular students of color from low-income families -- by supporting community-driven reforms led by grassroots education organizing groups. Maximizing collaborative potential has always been central to CPER's DNA, and is encoded in the Fund's vision, strategy, and operational structure. In sharing lessons learned by CPER funders, staff, and grantees over the Fund's eight-year lifespan, we hope to contribute to the conversation about how grantmakers can nurture collaborations that advance building social movements for opportunity and justice.