听力原文： The National Center for Education Statistics did its latest research and found that more than one million American students learned at home. That was more than two percent of the school-age population. The report said the number of home-schooled students had increased. In 1999, about 850,000 students were considered home-schooled. This meant they were taught at home instead of at school for at least part of their education. The students' time spent in public or private schools could not be more than twenty-five hours a week. Michael Viscardi, for example, has been taught mostly at home, but with advanced math classes at a local university. The researchers asked parents why they home-schooled their children. 31% said the most important reason was concern about the environment of the local schools. 30% said it was to provide religious instruction. 16% said they were not satisfied with the quality of the instruction in the local schools. Critics of home-schooling say children need to attend school to help them learn social skills. They also say that some home-schooled children do not get a very good education. Still, all fifty states and the District of Columbia permit home-schooling. But some require more parent preparation or student testing than other states do. (14)