This paper examines the effect of early childhood investments on college enrollment and degree completion. We use the random assignment in the Project STAR experiment to estimate the effect of smaller classes in primary school on college entry, college choice, and degree completion. We improve on existing work in this area with unusually detailed data on college enrollment spells and the previously unexplored outcome of college degree completion. We find that assignment to a small class increases the probability of attending college by 2.7 percentage points, with effects more than twice as large among blacks. Among those with the lowest ex ante probability of attending college, the effect is 11 percentage points. Smaller classes increase the likelihood of earning a college degree by 1.6 percentage points and shift students towards high-earning fields such as STEM (science, technology, engineering and medicine), business and economics. We confirm the standard finding that test score effects fade out by middle school, but show that test score effects at the time of the experiment are an excellent predictor of long-term improvements in postsecondary outcomes. We compare the costs and impacts of this intervention with other tools for increasing postsecondary attainment, such as Head Start and financial aid, and conclude that early investments are no more cost effective than later investments in boosting adult educational attainment.