The study reviewed in this report examined the impact of a summer literacy program on kindergarten and first-grade students who were at moderate risk for reading difficulties in one Pacific Northwest school district. The study took place through a limited expansion of an existing summer program for high-risk students that was modified to include moderate-risk students. Study authors randomly assigned 49 kindergarten students (25 intervention, 24 comparison) and 51 first-grade students (26 intervention, 25 comparison) identified as moderate-risk to either an intervention group that was invited to participate in the summer reading program, or a comparison group that did not receive the intervention. The final analytic sample consisted of 46 kindergarten students (24 intervention, 22 comparison) and 47 first-grade students (23 intervention, 24 comparison). The study found, and the What Works Clearinghouse (WWC) confirmed, a statistically significant positive effect of the summer school intervention on student outcomes in the fall of the implementation year for students in both kindergarten (effect size on the alphabetic assessment = 0.69) and first grade (effect size on the reading fluency assessment = 0.61). The research described in this report meets WWC evidence standards without reservations. Appended are: (1) Study details; (2) Outcome Measures for each domain; and (3) Study findings for each domain. A glossary is included. (Contains 2 endnotes.)