Motivated by potential financial savings, 4-day school weeks have proliferated across the United States in recent years, reaching public schools in 24 states as of 2019. The consequences of the 4-day school week for students, schools, and communities are largely unknown. This article uses district-level panel data from Oklahoma and a difference-in-differences research design to examine the causal effect of the 4-day schedule on school district finance and academic achievement. Results indicate that 4-day weeks decrease districts' federal revenues and their noninstructional and support services expenditures. Decreases are concentrated specifically in operations, transportation, and food services expenditures and amount to approximately 2.03% of the average 4-day district's budget. There is no detectable effect of the 4-day week on academic achievement.