You’ve probably noticed that it’s harder to think clearly after a long day of reading, writing, and arithmetic—in short, after a long day of thinking. For the most part, that’s not a particularly big deal, but a study out today in Proceedings of the National Academy of Sciences suggests it might matter to schools and their students. As it turns out, each hour that passes before starting a test drags scores down by a little bit, meaning students who take a test late in the day will perform noticeably worse.
A core assumption underlying academic achievement testing is that the tests measure, at least roughly, how much students have learned. Of course, that assumption isn’t really true; for one thing, there are persistent racial biases in academic testing. But, economists Hans Henrik Sievertsen, Francesca Gino, and Marco Piovesan wondered, could there be even more fundamental cognitive biases? Like, say, how tired students are when they take a test?
Educators should consider cognitive fatigue when planning the overall length of school days.
To answer that question, the trio analyzed scores from every student who took the Danish National Tests between the 2009–10 and the 2012–13 school years. That includes 10 tests in all—reading in grades two, four, six, and eight; math in grades three and six; and geography, physics, chemistry, and biology tests in grades seven and eight. In total, there were 2,034,564 test scores representing 570,376 students in 2,105 schools. Tests were given in three parts, presented to each student in random order, and lasted throughout the day, with breaks around 10 a.m. and noon.
Percentile rankings, which show where students rank on a 100-point scale, declined by about two-tenths of a point per hour on average, though how much scores dropped—and whether they dropped at all—changed throughout the day. Students who took a test at 9 a.m., for example, ranked 1.35 points lower than those who were tested on the same material at 8 a.m. Ranks increased 0.37 points after a 10 a.m. break, but dropped again by 0.58 points for tests taken at 11 a.m.
To put those results into context, the team also estimated the effects of parental income and other demographic measures. On average, taking a test one hour later in the day was about the same as parents making $1,000 (in American dollars) less, parents being educated one month less, or kids having about 10 fewer days of schooling—not large effects by any means, but important ones nonetheless.
Those results don’t mean schools should necessarily test students earlier in the day, Sievertsen, Gino, and Piovesan write. Instead, educators should consider cognitive fatigue when planning breaks and the overall length of school days, including test days, and whether it’s feasible for schools to adjust scores to account for the time of day the tests were taken.
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