Alexander Miranda, 12, works on a paper at KIPP Academy in Lynn, which has already started its school year. KIPP educators say a key to its success is an extended school day. KIPP students spend 9 1/2 hours a day in school during the year, about three hours longer than district schools. There are also 15 additional school days in the summer, and about 100 students voluntarily attend KIPP each Saturday for classes and extracurricular activities.