PARIS - To succeed at school or work, being a Sagittarius or an early Capricorn is not your best bet. This prediction isn't based on the stars, but on your birthday. A recent French study by Julien Grenet for the National Scientific Research Center (CNRS) found that those born in December are more likely to have a less successful schooling than those born 11 months earlier in January.

With obligatory school entry dates in France, end-of-the-year kids are younger and therefore less intellectually mature than their elders when taking exams, which results in lower grades. This weakness is most visible in primary school and among children from poorer families, but does not end there.

An 11-month interval makes a child lose seven places in a 30-student class ranking of first-graders, and five third-graders, according to the study. In first grade, those born toward the end of the year get grades that are 66% lower than those born in January. Though these problems decrease as students grow older, being born in December still costs a child three to four places in 6th grade and two at the end of middle school.

But the worst news to come from this study, first published in Le Monde, is that this liability risks following December kids throughout their lives. Grenet's study reveals that the French education system (which determines orientation at the start of high school and easily recommends repeating a year) amplifies the birth-month effect.

These schooling difficulties increase the children's chances of being left back, which in itself increases their chances of going to a technical high school. The probability of repeating a year is twice as high for 11-year-olds born in December. At 15 years of age, 51% of December-born students compared to 35% of those born in January have repeated a year. The study also found repeating is twice as likely for 11-year-olds from lower-class families.

Similar costs in other countries

Falling behind in school increases the probability by three points of leaving school with a professional-technical education diploma instead of a general education diploma. The birth month effect also has a bigger impact on men than women. Among men, being born later in the year reduces the overall level of degrees obtained. Among women, the birth month influences more specifically the type of degree (professional/general.) Women tend to go to school longer and more of them get a professional college degree.

The differences in diplomas has an impact on salaries, although minimal, Grenet found. Being born in December has a bigger influence on the degree level than on the type of academic training. People born in December receive slightly lower paychecks than those born in January, 2.3% for men and 0.7% in women. Le Monde estimated the shortfall at about 12,000 euros over a 42-year career. A December birthday also makes it harder to succeed at exams for civil service, and increases chances of being unemployed by 0.5%.

These inequalities aren't just a French phenomenon. In UK classrooms, the student entry into a grade falls between September 1st and August 31st. So those born in the summer face these same challenges. Some European countries have tried to tackle the issue, including the Netherlands' allowing those born toward the end of the year to stay in first grade for two years to give them a better chance at succeeding. But for Grenet, the solution is to adjust the grades of the youngest students in middle school according to their birth month.

Read the original article in French