Motivated by potential financial savings, four-day school weeks have proliferated across the United States in recent years, reaching public schools in 25 states as of 2018. The consequences of the four-day school week for students, schools, and communities are largely unknown. This paper uses district-level panel data from Oklahoma and a difference-in-differences research design to examine the causal effect of the four-day schedule on school district finance and academic achievement. Results indicate that four-day weeks decrease districts' federal and state revenues and their non-instructional and support services expenditures. Decreases are concentrated specifically in food services and transportation expenditures and amount to approximately 1.36% of the average four-day district's budget. I find no detectable effect of the four-day week on academic achievement.