The purpose of this study was to analyze P-20 partnerships in order to learn the best practices they employ to increase college access and persistence for under-represented students. This study adds to the literature by reaching beyond the collaborators and decision-makers who serve on partnership committees and include the individuals at the local level who carry out the work. A qualitative study was designed to learn how all of the stakeholders involved address the challenges inherent in inter-segmental collaboration. Semi-structured interviews were conducted with a cross-section of 29 participants from four partnerships in Southern California. The participants included teachers, professors, administrators, and counselors from the public PK-12 and higher education sectors. Additional data were collected from partnership meetings and site visits for each of the four partnerships. Findings from this study conclude that the three major challenges these P-20 partnerships face are: (1) a lack of trust within and across sectors, (2) a lack of time for partnership work, and (3) sustaining dynamic partnerships. Conversely, the three best practices uncovered were: (1) structure initiative-based committees with transparent reporting systems, (2) find champions for the work, and (3) focus on student needs.