Short boys are more likely to be held back a year at school than their taller classmates, research suggests.

The decision to hold children back a year may be influenced by their height as well as other factors such as their maturity or ability in the classroom, experts say.

They measured the height of almost 3,000 boys and girls aged between five and 12 years old from 24 different primary schools.

While girls were unaffected by height, the older boys in the classes - particularly the ones made to repeat a year - were shorter than their fellow pupils.

The researchers at the centre for community child health at the Royal Children's Hospital in Parkville, Australia, suggest that while the smaller boys may have been performing less well than their taller peers, their height may have "tipped the balance" in favour of keeping them back a year.

No relation

But they found no relation between the weight of children at birth and their likelihood to be held back a year - or "retained" - at school.

They also ruled out social and economic factors, race and parental education as factors in the findings, says a report in the journal Archives of Disease in Childhood.

The researchers found that the youngest third of each class was taller than the oldest third.

Two thirds of the children who had repeated a year at school were boys, the study found.

Dr Melissa Wake, who led the research, said: "When boys experience school difficulties, height may indeed be one factor influencing the final decision to retain.

"While the smaller boys may have been performing overall less well than the taller boys, it seems more likely that the short stature 'tipped the balance' for parents and teachers when making decisions."

Dr Wake said that previous research has shown that adults have a tendency to treat children at a level appropriate to their size rather than their age.

She added: "An awareness that children of smaller stature may be disadvantaged by such societal perceptions may help in correcting these inequalities."