This paper addresses the question of how to interpret evidence on the impact of full-day kindergarten resulting from different study designs, and provides guidance on how this evidence taken in tandem may inform the design and implementation of full-day kindergarten policies. Incorporating both experimental and quasi-experimental estimates on program impact, the study capitalizes on student assignment policies that allocated oversubscribed full-day kindergarten slots based on random lotteries and fixed cut-points on kindergarten readiness assessments, testing the causal impact on students' literacy skills at the end of the kindergarten year. The study uses data from eight school districts across Indiana: five districts that employed lotteries to assign students to full- and half-day kindergarten settings, and three districts that assigned the most academically needy student--on the basis of a cutpoint on a kindergarten readiness pretest--to oversubscribed full-day kindergarten slots. The districts are diverse in geographic location, size, and student composition. The intervention was assignment to--and participation in--full-day kindergarten, but notably, the student assignment policies from which the research designs are established also affect student composition in the classroom. The two sub-studies included in this paper employ experimental and regression discontinuity designs respectively. Experimental findings suggest that students who are assigned to--and those who participate in-- kindergarten in a full-day setting outperform their peers in half-day settings (0.31 standard deviations) in the same schools. In particular, findings reveal that nonwhite, predominately Hispanic students benefit (0.52 standard deviations) from full-day kindergarten in comparison to their half-day kindergarten peers. These heterogeneous treatment effects have implications for narrowing or closing the achievement gap early in formal schooling, and in fact constitutes 117 percent of the control group's race/ethnicity gap. Results from the districts that employed fixed cut-points to assign the most academically needy students to full-day kindergarten is not consistent with the experimental estimates. A figure is appended.