This year, the 14-year-old takes half his courses via the Web, completing homework on polynomials and Latin abbreviations from his bedroom desk looking out at the gentle slopes of Mount Diablo and a leafy cul-de-sac below. "I enjoy learning online more," said Ian, "especially since I don't have to lug books everywhere." The flexibility of Internet classes also suits his globetrotting lifestyle. During a month-long trip to England to visit his grandparents, Ian logged three-system matrices for math class. During frequent jaunts to the family's other home in Mexico, Ian can jump online at a neighbor's house to complete his English essays. "Wherever I have Internet," Ian said, "I can do online work." Like many things in modern teenage life, school is going virtual. An estimated 700,000 students in American public schools take classes online, according to a March study by Hunter College School of Education in New York.