Despite dramatic increases in the percentage of 5-year-olds enrolled in full-day kindergarten, initial discussions about whether to offer public full-day kindergarten are still controversial in many communities. This report examines claims about benefits and detriments of full-day kindergarten, presents research findings, and describes reasonable approaches to the issue for teachers and administrators. Following introductory remarks, the report details full-day kindergarten claims and counterclaims regarding benefits of extra instructional time, opportunities for enrichment activities, and reductions in child care costs for families, as well as disadvantages related to student adjustment and need for additional teachers. The report then summarizes reviews of full-day kindergarten research between 1970 and 1997 and describes two recent experimental or quasi-experimental studies. Among the conclusions about full-day kindergarten is that full-day students consistently progress further academically during the kindergarten year compared to half- or alternate-day students. There is tentative evidence that full-day kindergarten has stronger, longer-lasting academic benefits for children from low-income families. There is no current, strong evidence that academic achievement gains of full-day kindergarten persist beyond first grade. There is no evidence of detrimental effects of full-day kindergarten. The report indicates that further research is needed to examine the long-term impact of full-day kindergarten and recommends that half-day kindergarten remain an option for families who have educational resources, value time at home with their 5-year-olds, and desire a more gradual introduction to formal schooling. Implications for administrators, teachers, and parents are delineated. (Contains 26 endnotes, and a list of 26 additional resources and 9 related Web sites.) (KB)