Overall, children who spend time in full-day kindergarten programs are more likely than children who spend time in half-day kindergarten programs to devote time every day to reading, mathematics, and social studies. Research is inconclusive on longer-term impacts. Trends identified in this report include: (1) since 1977, the percentage of kindergarteners enrolled in full-day (in contrast to half-day) programs has nearly tripled, increasing from 28 to 77 percent between 1977 and 2013; (2) Asian and Pacific Islander kindergarteners are less likely than other kindergartners to be enrolled in full-day programs; (3) kindergarteners in the West are the least likely to be enrolled in a full-day programs (42 percent, compared with 23 percent in the Northeast, 18 percent in the Midwest, and 15 percent in the south); (4) in 2013, kindergarteners in low-income families and those in higher-income families were equally likely to be in full-day programs; and (5) in 2013, kindergarteners in public and private schools were equally likely to be in full day programs.