The four-day school week (4dsw) is growing in popularity, especially in rural areas across the western United States. RAND Corporation researchers addressed knowledge gaps about the 4dsw by conducting a large-scale study of the implementation and outcomes of the 4dsw that involved the collection of original data in numerous districts across Idaho, New Mexico, and Oklahoma, as well as administrative data from these and other states. The researchers analyzed both qualitative and quantitative data to compare the 4dsw and five-day school week (5dsw). The analyses resulted in mixed findings. Advocates of the 4dsw argue that the shorter week saves money, improves student attendance, and helps recruit and retain teachers in rural districts. Cost savings related to the four-day model were relatively small, but savings due to a 4dsw may be used to maintain the level of instructional expenses in the face of revenue shortages. There was no quantitative evidence that the 4dsw improved student attendance. Qualitative data supported the view that the model helps attract and retain teachers. Families and students reported highly valuing the extra time that the 4dsw allowed them to spend together, and the data showed that, overall, stakeholders experienced high levels of satisfaction with the 4dsw. However, a comparison of English language arts and math test scores showed that students on the 4dsw have lower scores, over time, when compared with peers on a five-day schedule. Given these mixed findings, communities are likely to make different choices about the 4dsw depending on their goals and the local context. [For the research brief, see ED615238. For Appendix C, see ED615239.]