The idea behind standardized testing is that everyone gets the chance to perform on the same test in the same circumstances. In an ideal world, this should create a system where everyone’s test results are a good indicator of their skills, learning, and hard work.

The reality, of course, is different. Standardized testing faces a host of criticisms, some more valid than others. But even if we assume that everyone walks into a standardized test with the same background, when the test happens matters. The timing of the test itself can have a marked impact on student scores, according to a new paper in PNAS.

The paper found that the later in the day a standardized test was held, the lower the scores were. That’s an important finding, given how much rests on standardized test results. These tests not only form the basis of education policy in countries all over the world, but they're often also used to decide how funding should be distributed among schools. And, most obvious of all, a test score can determine the course of a student’s life.

Cognitive fatigue

The study was based on children aged between eight and 15 years old who attended Danish public schools between 2009 and 2013. In 2010, the Danish Government introduced annual standard tests across all schools, with the goal of evaluating and improving the education system. Different subjects or skills are tested in different years, starting in the second grade. For the Danish system, this data set amounted to more than two million tests from 570,376 students across more than 2,000 schools.

Because there's existing evidence that mental resources get taxed throughout the day, the researchers thought it would be likely that tests taken later in the day would have lower scores, simply because students were more tired. In the schools they studied, the time of each student’s test was determined by their class schedule as well as computer availability, so there was a big spread in test times.

Overall, the results support what the researchers expected: test results declined throughout the school day. There was an important exception, though—students who took their tests immediately after a break not only recovered from the overall decline but actually had higher scores than students who took their tests first thing in the morning. This suggests that having a break before every test slot would actually result in improvements across the board.

There are weaknesses in a simple test like this. For example, there are various factors that impact children’s test results: family background, the physical health of the children, and their age (each test is taken by children who were born at different points within the same year, meaning that some are slightly older than others). There’s no obvious reason why children would have been grouped according to these factors when their test times are allocated, but it’s possible that things fall out that way for some reason.

The researchers looked at the data again to control for factors like these. Even individual students showed the same pattern of declining results across the day, with improvements after breaks. The effect was stronger for older children and for math tests. It also affected lower-performing students more than higher-performing students.

There’s also a question regarding whether the temporary boosts were caused by breaks, because the researchers didn’t have clear data on school break times. They knew what time Danish schools were likely to have breaks, but they received survey responses on break times from only about five percent of the schools they studied. When they looked just at those schools, though, the effect stuck around.

Real-world differences

Despite the wide-reaching implications of standardized testing, the authors note “it is not without bias.” The decline they found was small, but the links between standardized test scores and real-world numbers like parental income and education level allowed them to estimate how big the decline was in real terms. Each hour later in the day that a test is taken has an effect comparable to that child coming from a family with “1,000 USD lower household income, a month less parental education, or 10 [fewer] school days [before the test],” they write. That’s not negligible.

There’s more work to be done on figuring out how test scores change depending on who takes the test and when they take it. For older teenagers especially, it could be useful to look at the effect of circadian rhythms on results. For everyone, other factors like noise, hunger, and lighting could also make a difference.

But on the back of these results, the authors suggest that school systems should account for cognitive fatigue and breaks when they plan for school day schedules. More generally, we should probably consider how external factors can affect standardized test scores, given the importance we've assigned them.

PNAS, 2015. DOI: 10.1073/pnas.1516947113 (About DOIs).