A four-day school week (4dsw) is becoming more common, especially in areas across the western United States. States with large rural areas are spearheading this change. For example, Colorado, Idaho, Missouri, Montana, New Mexico, Oklahoma, and South Dakota have more than 500 districts using a 4dsw. The transition to the 4dsw and the debate over its effects have taken place largely in the absence of empirical evidence. To address this knowledge gap, a team of researchers from the RAND Corporation conducted a large-scale study of the 4dsw using data from 36 districts across Idaho, New Mexico, and Oklahoma. The study addressed two overarching research questions: (1) How is the 4dsw implemented?; and (2) What are the benefits and drawbacks of the 4dsw? This study, the largest of its kind to date, presents findings that can help inform choices by school, district, and state education leaders about the 4dsw model and develop policies or guide change as needed. Although this research can help promote understanding of how much the 4dsw affects outcomes, each community must ultimately decide how to weigh which outcomes matter the most. [For the full report, see ED615237. For Appendix C, see ED615239.]