Some findings are at once both evident and uncomfortable. For instance, students have a higher chance of passing an oral exam if it’s scheduled around noon. Not because they’re better prepared, or because the content is easier, or because the examiner is more lenient that day. Simply because of the time on the clock.

In a recent study, Vicario and colleagues analysed a whopping 104,552 oral exams at an Italian university, held between 8:00 and 16:00. The pattern they found is strikingly consistent: pass rates form a near-perfect bell curve, peaking at midday and dipping in the early morning and late afternoon. Even after correcting for course difficulty and credit weight, the effect remained. In fact, it was quite substantial—students at 12:00 were significantly more likely to pass than those at 8:00 or 16:00.

Why? The authors point to a mix of plausible explanations. On the student side: circadian rhythms and chronotype. Most students are biologically wired for later activity, meaning early morning performance may lag behind. Add in exam stress, poor sleep, and skipped breakfasts, and the odds stack up. On the assessor side: mental fatigue and ego depletion. After a long series of exams, or in the afternoon slump, assessors may be stricter, less sharp, or just cognitively tired. We’ve seen this before: a classic study of Israeli judges found that parole decisions were more favourable after breaks and meals, until fatigue set in and favourable rulings dropped.

That doesn’t mean assessors are being “unfair” on purpose. But it does mean the timing of decisions can sway outcomes, even in supposedly objective contexts. And that has implications. If your grade depends partly on whether your exam was at 11:00 or 15:00, that’s a problem. The researchers stop short of prescribing fixed exam hours, but they do suggest rethinking scheduling, including shorter sessions, more breaks, or aligning exam times with students’ chronotypes.

It also doesn’t mean we should now reschedule every exam to exactly 12:00. The study is correlational, based on one Italian university, and only includes oral exams — we don’t know if the same effect shows up in written tests, other countries, or online settings. Nor do we have data on student chronotypes, sleep, stress, or examiner fatigue — all likely candidates, but still speculative. And while the exams were randomly scheduled, we can’t fully rule out subtle biases in who ends up at which time slot. So yes, the pattern is real, but the why is still murky — and the what-to-do-about-it even more so.

This also raises a broader point: a lot of what we call “performance” isn’t just about ability. It’s about timing, context, energy, sleep, stress, and all the invisible stuff we tend to ignore when judging others—or ourselves. Perhaps we should acknowledge that assessments are not purely meritocratic, as the clock on the wall suggests.

Abstract of the study:

The influence of timing on decision-making processes has garnered significant attention across various domains, yet its impact on academic assessment remains under investigated. While previous research has suggested time-of-day effects on judicial decisions, methodological limitations have restricted the generalizability of these findings. Here, we present a comprehensive analysis of 104.552 oral exams conducted at an Italian university, revealing a robust relationship between exam timing and academic outcomes. Our results demonstrate a Gaussian distribution of passing rates throughout the day, with a significant peak at midday. This pattern persists after controlling for exam difficulty and other potential confounding factors, suggesting an intrinsic time-dependent bias in the evaluation process. Our findings not only corroborate previous research on the influence of timing on decision-making but also extend it to the realm of academic assessment. These results have profound implications for educational policy and practice, highlighting the need for strategic exam scheduling to optimize student performance and ensure equitable evaluation.