The paper is an overview of research by EPA's Air and Energy Engineering Research Laboratory (AEERL) on radon mitigation in 47 schools since 1988. The structural and heating, ventilating, and air-conditioning (HVAC) system characteristics of the research schools are presented, along with the mitigation techniques implemented in the schools. Research discussed includes recent and on-going projects in Colorado, Maine, Maryland, Ohio, South Dakota, Tennessee, and Virginia. Initial research focussed on the application of active subslab depressurization (ASD) to school buildings, and recent research has emphasized the ability and limitations of using HVAC systems to reduce radon levels in schools. A goal of future projects is to compare the effectiveness of the two techniques in the same building. Slab-on-grade is the most prevalent substructure in AEERL's research schools and, depending on pressure field extension, ASD systems have been recommended for radon control in many of them. In schools where they have been installed, ASD systems have performed well and are currently being evaluated for long-term performance. The distribution of HVAC system types in these schools is about a third central air handling systems, a third unit ventilators, and a third that do not supply conditioned outdoor air (i.e., fan coil units or radiant heat).