For more than 30 years, Medicaid has played a key role in paying for school health services. As the source of health insurance for 40 percent of children across the country, Medicaid helps ensure low-income children receive healthcare they need to be healthy and ready to learn. Today, new opportunities exist to enhance the role that Medicaid plays in school, creating a sustainable source of revenue to support school-based health services, including mental health services. Examples of services Medicaid might pay in states include but are not limited to: nursing services; mental health services; occupational, physical, and speech therapy; physician services; optometry services; respiratory therapy; dental services; diagnostic, screening, preventive, and rehabilitative services; and nutritional services. Chief state school officers can play an important role in leveraging these opportunities in their state to ensure all students have the supports they need to achieve academically. This primer explores what Medicaid is, what it covers--in and out of school, --and new opportunities for expanding school Medicaid programs statewide.