Virtual charter schools--public charter schools that operate entirely or mostly online--largely depend on self-paced, asynchronous (accessed at any time) instruction and often rely on parents to act as instructors, according to the US Government Accountability Office's (GAO's) review of a nationally representative sample of virtual charter school websites and interviews with school officials. Enrollment in virtual schools has increased faster than enrollment in other types of public schools in recent years. This trend was accelerated by COVID-19, which prompted an increase in distance learning. Virtual charter schools account for about 70 percent of students enrolled in virtual schools. GAO was asked to review virtual charter school operations and oversight. This report examines: (1) how virtual charter schools provide student instruction; (2) how virtual schools' academic proficiency and participation rates on state tests compare to other school types; and (3) the extent to which virtual charter schools' operations present challenges for state and federal oversight. GAO interviewed state and charter authorizer officials from four states collectively serving over 50 percent of all virtual charter school students in 2019-2020. GAO analyzed federal data on virtual charter school enrollment and academic outcomes; reviewed a nationally representative sample of virtual charter school websites; reviewed school financial information; and interviewed federal and school officials.