This article explores challenges in starting, developing, and incorporating partnerships between the secondary and postsecondary education sectors. We use qualitative data from site visits at high schools, district offices, and state colleges across six Florida counties to identify the types of challenges educators faced in various phases of partnership around college readiness. Then we provide empirical evidence to support a conceptual framework based on a partnership model, which demonstrates that social capital and organizational capital are needed to create "partnership capital" to initiate and sustain cross-sector partnerships. We find that whereas considerable collaborative resources are available to help higher performing students prepare for selective universities, there is much less collaboration around improving college readiness among students who lack the requisite skills. [For the corresponding grantee submission, see ED593092.]