Virtual school programs--especially online high school courses--are gaining traction in school districts around the country. While offering online courses was once the exclusive province of large state, nonprofit and for-profit organizations and companies, districts and even individual schools are now starting virtual schools of their own. Not only are more districts launching online courses, but the definition of virtual schooling also has expanded. That includes the growing popularity of "flipped classrooms," in which students go online for video lectures and demonstrations outside of class and spend class time working with their teachers individually or in groups. Also, the burgeoning "bring your own device" movement in many districts has brought online learning into the classroom, as students search Web sites for information, collaborate virtually, or work on interactive exercises under the direction of their classroom teachers. A crop of virtual high schools, meanwhile, also has taken root, offering a four-year online education and diplomas. Offering an entire online high school education is becoming an increasingly attractive proposition to districts because the per-pupil expenditure can be a third lower than at brick-and-mortar high schools. But as district leaders charge ahead with implementing or expanding online programs, they might do well to heed the lessons learned by successful predecessors in critical areas, from course quality and teacher training to technology and administration, where the problems can be anything but virtual.