Within the past decade, state-funded Pre-Kindergarten has roughly doubled in its coverage of 4-year-olds, and further large-scale expansion of Pre-K programs, with state, local or federal funding, continues to be debated. Although research has shown that Pre-K can increase test scores and dramatically improve life outcomes, at least for some programs at some places and times, existing studies have generally focused on small or state-specific programs that may not sufficiently capture program heterogeneity and thus may not generalize to other areas or programs. In this paper, we draw upon multiple data sources to exploit variation in enrollment in public Pre-Kindergarten programs across time and place to examine the effects of these programs on standardized test scores and other academic outcomes. Our paper is unique in its scope: our data cover the last two decades, span nearly all states, and allow for intrastate variation in Pre-K. We find no evidence that the average state program affects the average student's test scores, assignment to special education, or grade retention. Our estimates are precise enough to rule out impacts as small as 2 percentiles for full Pre-K saturation. However, these averages conceal some important heterogeneity. In states that other studies have found to have high-quality Pre-K programs, we find positive effects on average math test scores. For majority-Black districts, the average Pre-K program yields sizable effects on both math and reading. (author abstract)