The first part of the two-part paper discusses radon entry into schools, radon mitigation approaches for schools, and school characteristics (e.g., heating, ventilation, and air-conditioning--HVAC--system design and operating) that influence radon entry and mitigation system design. The second part discusses specific mitigation systems that were installed by the U.S. EPA in four Maryland schools. HVAC systems in schools vary considerably and tend to have a greater impact on pressure differentials--and consequently on radon levels--than do heating and air-conditioning systems in houses. If the HVAC system induces a negative pressure relative to the subslab area, radon can be 'pulled' into the building. If the HVAC system pressurizes the building, it can prevent radon entry as long as the fan is running. However, school HVAC systems are normally set back or turned off on evenings and weekends and, even if the HVAC system pressurizes the school during operation, indoor radon levels may build up during the setback periods. The primary mode of radon entry into a school with significantly elevated radon levels is normally from soil gas that is drawn in by pressure differentials between the soil surrounding the substructure and the building interior.