School districts across the United States are implementing four-day school weeks. This study looks at the relationship between student achievement in the four-day school week compared to student achievement in the five-day school week. This analysis focused on a common criteria referenced test given to all students over a period of seven years in a single western state. The study provided conclusive evidence that students in the four-day week did not performed as well, over time, when compared to students in the traditional five-day week settings.