Unless you’re a keen believer in horoscopes, you might think that the month you’re born in has little bearing on your personality, your potential or your success in later life.

But you’d be wrong. Research has shown that because they are 11 or 12 months less mature than some of their classmates when they start school, children born in the summer months of July and August often lag behind their peers for the rest of their lives. They suffer from lower marks, are less confident and are more likely to be unhappy.

Rosie Dutton, the mother one of these ‘summer babies’, was so concerned about the effects of being the youngest in the class that she fought an 18-month battle with her local council in Staffordshire and has won a landmark ruling to start her daughter's education one year later than usual.

[Related story: From reading to writing: your children’s educational milestones]

Campaigners predict a floodgate of similar cases; estimating that as many as 250,000 parents of ‘rising five’ children will want to hold them back a year from reception class. And they do have these very good arguments in their favour.

They’re just not ready

“There is evidence that some children who have just turned four are not developmentally ready for the current reception curriculum,” says Tammy Campbell, researcher at the University of London’s Institute of Education (IoE).

“The fact that a parent has been able to delay her summer-born daughter starting reception is therefore positive – but this should be possible for any child who is not yet ready for reception.

Exercising this right is currently dependent on parents having the time, knowledge and resources to fight for a delay to their children’s start dates.”

They’re a quarter of a lifetime behind

Dr Rebecca Chicot, co-founder of the Essential Parent Company, is quick to agree this new ruling is critical.

"My youngest child was born premature on August 30, she wasn’t due until September 26 and I remember her having her fourth birthday only two days before she started school. She was the youngest, smallest child in the school.

Some of her classmates were a year older than her which means they’d been alive, growing and developing 25% longer than her.

“The differences in developmental stage between a four-year-old and a five-year-old are very big in these early years when brain development is huge.”

It’s a waste of talent

“A study of professional ice hockey players in Canada showed all the top players were born in the first week of September,” Chicot adds.

“This means that gifted children born in the remaining 51 weeks missed out on selection due to the arbitrary school term dates. It is a waste of talent and based not on children’s educational needs or abilities but on bureaucracy and administration.”

They’re bottom of the class

Not always, of course, but often. A recent study from the IoE showed that the youngest children in a school year are far more likely to be placed in the lowest ability groups than autumn-born pupils.

By the age of seven, September-born children were nearly three times as likely to be in the top stream as those born in the following August.

They do worse in exams

The trend continues with age too: researchers at the Institute for Fiscal Studies (IFS) revealed that August-born pupils achieved worse exam results, on average, than children born in September - simply because they were 11 months younger.

They’re less likely to go to a top university

Even out of school education, they effects continue, with another study showing August-born teenagers are 20% less likely to win a place at a top UK university than their class-mates born in September.

They’re less confident

Sadly, the idea of summer babies being all happy and bright to match their birth weather doesn’t always prevail. Research has also found summer-born children are less confident than their autumn-born peers, and are less likely to believe in their own ability or think that they have control over their lives.

They’re often bullied

The sorry list goes on: it’s been reported that children born in August are more than twice as likely to report being always unhappy at school, and twice as likely to report being bullied all the time at the age of seven.

Do you think summer-born children are at a disadvantage? Post your thoughts in the Comments below.