This study reports on the implementation of Gateway to College, a program whose mission is to serve students who have dropped out of high school, or who are at risk of dropping out of high school, by allowing them to earn a high school diploma and credits toward a postsecondary degree. Gateway to College is uniquely ambitious in providing struggling students with opportunities often reserved for the highest achievers; it believes that high expectations and the right support can lead to more students completing high school and transitioning to college. This report has two main goals: (1) Provide an in-depth description of the Gateway to College model, and more precisely define the youth population served by the program; and (2) Describe the implementation of the Gateway to College model at three program sites, assess the extent to which it is implemented as designed at those sites, and draw lessons for other Gateway to College programs. This study finds that, at a broad level, the three study sites implemented the Gateway to College model as designed. However, Gateway to College struggled with finding the right balance between being flexible and providing concrete guidelines for implementation. The following are appended: (1) Lessons Learned About Student Outreach; and (2) Data-Collection Activities.