The 4-H youth development organization is a complex public--private partnership between the U.S. Department of Agriculture's National Institute of Food and Agriculture, the nation's Cooperative Extension system and National 4-H Council, a private, nonprofit partner. The current article is focused on a partnership approach to the evaluation of a national 4-H Science initiative that engaged both internal and external evaluators as well as key stakeholders. While external evaluators are valued for their relative lack of bias and independence, internal evaluation has been the predominant strategy used by the Cooperative Extension system. For this evaluation, we adopted a hybrid approach that teamed an external evaluation firm with a team of internal evaluators and key stakeholders. We discuss specific strategies and approaches that we developed to implement this approach in the 4-H youth development organization and offer suggestions for how it might be useful in other complex, multipartner organizations.