Low-income youths enroll at postsecondary institutions less frequently, drop out more often, are less likely to return after dropping out, and are less likely to attain a postsecondary degree than their more affluent peers. It is therefore important to understand how low-income youths develop the capacity to persist in the postsecondary setting. This article explores how contextual supports contribute to low-income (and predominantly racial/ethnic minority) youths' educational expectancies and postsecondary persistence. The authors examined these questions by applying structural equation modeling to a longitudinal panel of youths surveyed 3 times over a 5-year period, while controlling for academic achievement, age, and gender. The obtained structural model suggests meditating "chains" by which parents and peers foster educational expectancies and postsecondary persistence over time. This article suggests that precollegiate contexts and expectancies clearly matter in explaining how low-income youths progress through intermediate checkpoints--postsecondary persistence--on the path to degree completion. (Contains 3 tables and 2 figures.)