Background: Parental Medicaid eligibility has been shown to be linked to positive academic and school outcomes for children. However, the impact of adult Medicaid expansion on children's school absenteeism is largely unexplored in the literature. The aim of this study was to examine whether Medicaid expansion for adults under the Affordable Care Act (ACA), affected school absenteeism of children. Methods: This study used data from the National Survey of Children's Health 2016 to 2017 and the difference-in-differences method. Results: The decrease in the predicted probability of missing 11 or more school days in Louisiana, after Medicaid expansion, among school-going children from low-income families, was greater by 18 percentage points (p = 0.007), as compared to the decrease in the predicted probability of missing 11 or more school days in the neighboring nonexpansion states of Texas and Mississippi. Conclusions: The positive impacts of Medicaid expansion are not limited to adults, but also extend to children's school absenteeism.