
In the 1998–99 school year, 61 percent of all U.S. schools that have a kindergarten program offer at least one full-day kindergarten class and 47 percent offer at least one half-day class. Overall, 56 percent of kindergarten children attend a full-day program (not shown in figures).1
A large majority of both full-day and half-day classes spend time each day on reading and language arts activities (97 and 96 percent, respectively). Other academic subjects, however, are more likely to be taught every day in full-day classes. Compared with half-day classes, a larger percentage of full-day classes spend time each day on mathematics (90 vs. 73 percent), social studies (30 vs. 18 percent), and science (24 vs. 10 percent) (figure 1).

On days when reading is taught, 31 percent of full-day classes spend more than an hour and a half on reading per day compared to 10 percent of half-day classes. On days when mathematics is taught, 21 percent of full-day classes spend more than an hour doing mathematics activities compared to 9 percent of half-day classes (not shown in figures).
The ECLS-K children were assessed in reading/language arts and mathematics in the fall and in the spring of the kindergarten year. Children in full-day programs, on average, make greater gains in their reading achievement scores from fall to spring (10.6) compared to those in half-day classes (9.4) (figure 2).

Children in full-day programs, on average, make greater gains in their mathematics achievement scores from fall to spring (8.6) compared to those in half-day classes (7.8) (figure 3).

The differences in achievement gains associated with program type are not only apparent when simple comparisons of gains are made (figures 2 and 3), they persist when the comparisons take into account other important child and class characteristics. Findings from a multi-level regression analysis indicate that children in full-day classes make greater gains in both reading and mathematics compared to those in half-day classes after adjusting for gain score differences associated with race/ethnicity, poverty status, fall achievement level, sex, class size, amount of time for subject area instruction, and the presence of an instructional aide.
1 Estimates here and elsewhere in the indicator are not adjusted by other child, class or school variables unless noted.