Background: This study investigates how the Medicaid Expansion of the Affordable Care Act affected state high school dropout rates. Methods: This study relies on a differences-in-differences estimation strategy that is common in program evaluation, especially in education. This method replicates in a regression framework a classic pre-test post-test comparison group quasi-experimental design. The analysis is conducted at the state level, which reduces the precision of the estimates. Results: States that adopted the Medicaid Expansion had a 0.658 percentage point greater reduction in dropout rates than non-Expansion states in the year of Medicaid implementation. A back-of-the-envelope calculation suggests that if all the remaining non-Expansion states adopted Medicaid, there would be a decrease of over 92,500 youths who drop out of high school, representing a drop of 11.2% in the number of dropouts in these states. Conclusion: The Medicaid Expansion of the Affordable Care Act is more than just a health insurance program; it is a dropout prevention program.