The ACT is a lengthy, high-stress standardized exam that over a million students will prepare for and take each year. On national test dates, the test is always administered on Saturdays, and always on Saturday MORNINGS. There is a reason for this: data shows that students test best in the morning. Here, we’ll walk you through why that is.

The day of the ACT exam, students are directed to report to the testing center no later than 8:00 AM, and testing begins promptly at 8:30 AM. While that’s not as early as some students begin school, that’s still pretty early in the morning. Not to mention that students will then test for approximately 3 hours straight. That’s a lot to conquer on a Saturday morning. So, why not test later in the day?

As it turns out, there is a pretty key reason that standardized tests are administered in the morning: FATIGUE.

Why are standardized tests conducted in the morning?

Think back to a typical day at your high school. You moved from one class to the next, back-to-back-to-back. Do you remember how you felt by the end of the day? Chances are you were physically exhausted. A day full of learning and engaging in class is a tiring thing, and it would just so happen that there are now studies that prove just that.

So it turns out cognitive fatigue—a.k.a. your brain getting tired—is a real thing that affects student performance. The longer a student is cognitively engaged and learning, the more tired they will become. This would definitely explain why students can be physically tired after a long day at school, even if they’ve just been sitting in a desk all day.

Studies out of Denmark show that later testing start times correlate with lower overall testing scores. In contrast, early morning testing results in the highest test scores reported. In fact, for each hour later in the day that a test is given, the lower students’ average scores become. For this reason, standardized exams are meant to be the very first task that students engage their brains in on the morning of test day. There’s no time for a student to go and tire out their brain before showing up to the testing center at 8:00 AM.

Cognitive fatigue is sometimes considered when drafting new and modified education policy in hopes of bettering the education system for students, parents, and faculty. Cognitive fatigue is considered when determining things like school start times, as well as standardized testing times. Cognitive fatigue is a big factor in why standardized exams are conducted so early in the morning.

This makes quite a bit of sense when you think about it. Students wake up with a fresh brain that is ready to be used. Sleep is another crucial aspect of successful testing — it recharges the brain and body and prepares the student to complete 3 hours of testing without becoming overly cognitively fatigued. This is why it is not recommended that students ever pull an “all-nighter” studying for any exam — ACT or otherwise. Depriving your body of sleep is likely to cause you to do WORSE on an exam than getting a good night’s sleep and cutting your study time off early.

Check out these things we recommend students DO and DON’T do the night before the ACT. (Hint: SLEEP is something students SHOULD do!)

What can I do with this information?

This research doesn’t suggest that students ONLY perform best on tests like the ACT in the morning. Rather, it suggests that PEOPLE perform best on ANY COGNITIVE TASK in the morning, before their brain has been overloaded and exhausted with information and tasks.

Your high schooler could use knowledge of cognitive fatigue to their advantage…While you can’t always determine what time your student has a certain class or when they have time to do their homework, sometimes they could be strategic with their work outside the classroom. Students will find more success with studying earlier in the day than they will later, when their brain is tired from the day. Encourage your student to spend weekend mornings studying and doing homework, rather than waiting until the very last minute on Sunday night. Similarly, some students prefer to wake up early and study before school and find this more productive than evening studying as well. Each student is different, but the data suggests that all students could benefit (to some small extent) from scheduling cognitively taxing tasks for earlier in the day.

Interested in further exploring this topic? Check out this study of Danish students’ cognitive fatigue affecting standardized testing.