If you want to give your child the best start in life, try to conceive around the end-of-year holidays—at least if you live in a country where the school year starts in September. A new study has found that the older you are at the start of the school year, the more likely you are to excel in school, and in pretty much the rest of your life.

Early childhood experiences stay with us way longer than we might want, and what happens to us as children can dictate how we end up as adults. A new study investigated how the month of birth affects academic success and found that children born in September tend to do the best in school, while those born in August tend to struggle the most. However, the reason for this has less to do with astrological traits than with how old children are at the beginning of the school year.

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Results showed a very slight difference in average test scores between students born in August and those with September birthdays—a 0.2-point difference. However, over the course of the entire school career, these few tenths of a point can have a significant effect. For example, in addition to doing better in school, September babies were more confident, more likely to attend college and less likely to spend time in juvenile detention—at least in the state of Florida.  

For the study, a team from the University of Toronto, the University of Florida and Northwestern University looked at data of around a million public school students in Florida born between 1994 and 2000. The team paid close attention to the differences between students born in August and those born in September, as this was where the biggest test score gap occurred. Even when taking other factors into account, such as a mother’s education, poverty at birth, race and school quality, there remained a slight, yet stable, difference in test scores for September babies versus August babies.

Children's economic backgrounds also played a big role in whether their birthmonth would affect their education. Children from more affluent backgrounds did not really suffer much from being slightly younger than their classmates, but children from poorer backgrounds struggled more to keep up.

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The researchers noted that this is likely because children from more affluent families who may struggle in kindergarten are more likely to be held back a year to allow them to catch up. This opportunity is not as readily available to children from poorer families.

These results aren't necessarily telling parents how to plan their families; rather, they highlight a possible advantage in holding back children when it's necessary, and what can occur if they get lost in the shuffle because they're not quite ready.

“We show that the percent of children redshirted [held back] is positively related to the average test score level," the study concluded. “These findings indicate that school districts where redshirting and early grade retention are higher have smaller relative age gaps in test scores.”