An experimental curriculum focused on nonfiction texts helped improve the reading skills of some New York City students, a new study shows. The three-year study tracked about 1,000 students from kindergarten through second grade, half of whom used a program devised by the Core Knowledge Foundation, with the others using a "balanced literacy" approach. The study, conducted by the city's Education Department and funded by a charity, found students using the Core Knowledge curriculum scored higher in reading comprehension as well as social studies and science.