This investigation addressed 3 questions about the long-term effects of early school experiences: (a) Is participation in small classes in the early grades (K–3) related to high school graduation? (b) Is academic achievement in K–3 related to high school graduation? (c) If class size is related to graduation, is the relationship explained by the effect of participation in small classes on students’ academic achievement? The study included 4,948 participants in Tennessee’s class-size experiment, Project STAR. Analyses showed that graduating was related to K–3 achievement and that attending small classes for 3 or more years increased the likelihood of graduating from high school, especially among students eligible for free lunch. Policy and research implications are discussed.