Is four less than five? Effects of four-day school weeks on student achievement in Oregon

The achievement impacts of educational input quality have been well documented, but the quantity of exposure to the school environment – as measured by instructional time – also has profound impacts on students. This study examines the achievement impacts of a key instructional time reducing cost savings policy – the four-day school week. Using 3rd through 8th grade test scores from Oregon from 2005 to 2019 in a difference-in-differences analysis, I find that math test scores decrease by between 0.037 and 0.059 standard deviations and reading scores decrease by between 0.033 and 0.042 standard deviations following the switch to the four-day school week. It appears that reductions in time in school, which amount to three to four hours per week, largely drive these achievement declines. Using four-day school week adoption as an instrument for weekly time in school, I find that a one-hour increase in weekly time in school leads to a 0.018 standard deviation increase in math achievement and a 0.006 standard deviation increase in reading achievement. Finally, I compare the cost savings-achievement trade-off of the four-day school week with other traditional cost savings approaches and find that the four-day school week yields a comparable cost savings-achievement trade-off to many of these other interventions.