Studies have shown that math skills in early childhood are uniquely and strongly predictive of later outcomes across a range of domains and well into adulthood, including the likelihood of graduating from high school and college completion. The Making Pre-K Count and High 5s studies were designed to rigorously test the short- and long-term effects of improving children's math experiences in prekindergarten (pre-K) and kindergarten. Making Pre-K Count provided pre-K teachers in New York City with a high-quality, evidenced-based math curriculum (Building Blocks) and ongoing teacher training and coaching. The Making Pre-K Count study compared students who were exposed to this curriculum with their peers in pre-K as usual in public school and community-based sites. The High 5s math program was developed to offer children who had received Making Pre-K Count in pre-K in public schools hands-on, supplemental math enrichment in small groups, or clubs, outside of regular instructional time in kindergarten. The High 5s study compared students assigned to Making Pre-K Count in pre-K and High 5s in kindergarten with children assigned to Making Pre-K Count in pre-K and kindergarten as usual. Taken together, the Making Pre-K Count and High 5s studies present new evidence about the long-term effects of early math interventions on children's later outcomes. Early math enrichment experiences can lead to lasting gains for children across a variety of outcome domains, even years later. The findings suggest that high-quality early math instructional practices could make a difference, particularly for children with the greatest need.