You can lose a letter grade just because your exam was in the morning or because of Daylight Saving Time, even if you know the material.
SSRN · March 13, 2026 · 6410081
Why it matters
We assume exams measure intelligence or preparation, but this analysis of 400,000 grades shows that scheduling is a massive hidden variable. Students perform demonstrably worse in the morning and during the week after the clocks change, suggesting that university rankings are partially just a measure of who is less sleep-deprived.
From the abstract
We study the effect of exam timing on academic performance among Dutch university students. Analyzing 400,055 grades from 24,280 students across seven academic years (2017/2018 – 2023/2024), we test whether students, in particular younger students, perform worse during morning exams. Additionally, we use the start of the Daylight Saving Time to help identify whether this effect is driven by sleep deprivation. We show that students perform worse during morning exams and in the week following the