The Danger of Being the Youngest Kid in Class

A Japanese study finds suicide is more common among students with birthdays just prior to school eligibility cutoff dates.
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(Photo: li jianbing/Shutterstock)

(Photo: li jianbing/Shutterstock)

More than 25,000 Japanese men and women took their own lives last year. While that doesn't qualify the country for the number one spot—that dubious title goes to Guyana—it remains a serious problem. Now, researchers report, they've found a surprising contributor to suicide in Japan: being relatively young for one's grade in school.

Most systems have a cutoff date for starting school. For example, if you're six years old by the time September rolls around in a given year, you're most likely going to start school that year. (If you're five, you still get to stay home with your parents.) As a result, kids with August birthdays are generally going to be the youngest in their classrooms, while those with September birthdays will be the oldest.

Between 1989 and 2010, about one in every 800 of those between the ages of 15 and 25 took their own lives, but that number is higher for people born earlier in the year.

Those relative age differences in school might seem fairly innocuous, but past research suggests they can have a significant, lasting impact on people. Around the world, those younger kids fare worse on standardized tests and eventually make less money as adults, factors which could contribute to depression and eventually suicide.

Still, observers aren't sure whether a direct link between relative age and suicide exists—a gap in the academic literature that Tetsuya Matsubayashi and Michiko Ueda have now begun to fill. To explore this question, they took advantage of Japan's rather strict birthday cutoff rules. Unlike American schools, the cutoff date is the same across all of Japan, and it's harder to get around: If you're six years old by the time school starts and you don't have a serious medical condition, you're going to school. That, the researchers argue, makes it pretty straightforward to ask how relative age within the classroom could affect suicide rates.

Analyzing data compiled by the Japanese Ministry of Health, Labour and Welfare, Matsubayashi and Ueda discovered that a kid's birthday really does have an impact on suicide. Between 1989 and 2010, 0.126 percent—about one in every 800—of those between the ages of 15 and 25 took their own lives, but that number is higher for people born earlier in the year. Those with birthdays within seven days leading up to April 2nd (the day the school year starts in Japan) killed themselves at a rate 0.034 percentage points higher compared with those born in the following week—a substantial difference, considering the baseline rate of 0.126 percent.

"Given that education at the early stage of life plays an important role in people’s future well-being, the arbitrary cutoff of school entry will generate a life-time disadvantage by the timing of birth for a non-trivial number of people," Matsubayashi and Ueda write. "To alleviate the negative consequences of the arbitrary cutoff, the government has a few policy options, such as allowing late entry to primary school or special assistance to those born just before the cutoff at the early stage of primary education."

Quick Studies is an award-winning series that sheds light on new research and discoveries that change the way we look at the world.

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